diff --git a/js/src/TraceLogging.cpp b/js/src/TraceLogging.cpp
index 80b07fbe26b8..82542774fd0c 100644
--- a/js/src/TraceLogging.cpp
+++ b/js/src/TraceLogging.cpp
@@ -90,17 +90,17 @@ const char* const TraceLogging::typeName[] = {
     "e,b",  // engine baseline
     "e,o"   // engine ionmonkey
 };
-TraceLogging* TraceLogging::loggers[] = {NULL, NULL, NULL};
+TraceLogging* TraceLogging::loggers[] = {nullptr, nullptr, nullptr};
 bool TraceLogging::atexitSet = false;
 uint64_t TraceLogging::startupTime = 0;
 
 TraceLogging::TraceLogging(Logger id)
   : nextTextId(1),
-    entries(NULL),
+    entries(nullptr),
     curEntry(0),
     numEntries(1000000),
     fileno(0),
-    out(NULL),
+    out(nullptr),
     id(id)
 {
     textMap.init();
@@ -111,12 +111,12 @@ TraceLogging::~TraceLogging()
     if (entries) {
         flush();
         free(entries);
-        entries = NULL;
+        entries = nullptr;
     }
 
     if (out) {
         fclose(out);
-        out = NULL;
+        out = nullptr;
     }
 }
 
@@ -137,7 +137,7 @@ TraceLogging::grow()
 }
 
 void
-TraceLogging::log(Type type, const char* text /* = NULL */, unsigned int number /* = 0 */)
+TraceLogging::log(Type type, const char* text /* = nullptr */, unsigned int number /* = 0 */)
 {
     uint64_t now = rdtsc() - startupTime;
 
@@ -149,7 +149,7 @@ TraceLogging::log(Type type, const char* text /* = NULL */, unsigned int number
     }
 
     uint32_t textId = 0;
-    char *text_ = NULL;
+    char *text_ = nullptr;
 
     if (text) {
         TextHashMap::AddPtr p = textMap.lookupForAdd(text);
@@ -248,9 +248,9 @@ TraceLogging::flush()
             exit(-1);
         }
 
-        if (entries[i].text() != NULL) {
+        if (entries[i].text() != nullptr) {
             free(entries[i].text());
-            entries[i].text_ = NULL;
+            entries[i].text_ = nullptr;
         }
     }
     curEntry = 0;
@@ -279,7 +279,7 @@ TraceLogging::releaseLoggers()
             continue;
 
         delete loggers[i];
-        loggers[i] = NULL;
+        loggers[i] = nullptr;
     }
 }
 
diff --git a/js/src/TraceLogging.h b/js/src/TraceLogging.h
index 3a3ad82f8cea..0b93542738f8 100644
--- a/js/src/TraceLogging.h
+++ b/js/src/TraceLogging.h
@@ -102,7 +102,7 @@ class TraceLogging
     TraceLogging(Logger id);
     ~TraceLogging();
 
-    void log(Type type, const char* text = NULL, unsigned int number = 0);
+    void log(Type type, const char* text = nullptr, unsigned int number = 0);
     void log(Type type, const JS::CompileOptions &options);
     void log(Type type, JSScript* script);
     void log(const char* log);
diff --git a/js/src/builtin/TestingFunctions.cpp b/js/src/builtin/TestingFunctions.cpp
index f9b585414865..487e418e82e3 100644
--- a/js/src/builtin/TestingFunctions.cpp
+++ b/js/src/builtin/TestingFunctions.cpp
@@ -830,7 +830,7 @@ DumpHeapComplete(JSContext *cx, unsigned argc, jsval *vp)
     CallArgs args = CallArgsFromVp(argc, vp);
 
     DumpHeapNurseryBehaviour nurseryBehaviour = js::IgnoreNurseryObjects;
-    FILE *dumpFile = NULL;
+    FILE *dumpFile = nullptr;
 
     unsigned i = 0;
     if (argc > i) {
diff --git a/js/src/jit/AsmJS.cpp b/js/src/jit/AsmJS.cpp
index beb11b624678..b786e2acb62c 100644
--- a/js/src/jit/AsmJS.cpp
+++ b/js/src/jit/AsmJS.cpp
@@ -5081,7 +5081,7 @@ class ParallelCompilationGuard
 {
     WorkerThreadState *parallelState_;
   public:
-    ParallelCompilationGuard() : parallelState_(NULL) {}
+    ParallelCompilationGuard() : parallelState_(nullptr) {}
     ~ParallelCompilationGuard() {
         if (parallelState_) {
             JS_ASSERT(parallelState_->asmJSCompilationInProgress == true);
diff --git a/js/src/jit/IonBuilder.cpp b/js/src/jit/IonBuilder.cpp
index 9ad69d6c55b3..7e8620d1023e 100644
--- a/js/src/jit/IonBuilder.cpp
+++ b/js/src/jit/IonBuilder.cpp
@@ -7777,7 +7777,7 @@ IonBuilder::freezePropTypeSets(types::TemporaryTypeSet *types,
             continue;
 
         // Walk the prototype chain. Everyone has to have the property, since we
-        // just checked, so propSet cannot be NULL.
+        // just checked, so propSet cannot be nullptr.
         while (true) {
             types::HeapTypeSetKey property = type->property(NameToId(name));
             JS_ALWAYS_TRUE(!property.notEmpty(constraints()));
diff --git a/js/src/jit/IonBuilder.h b/js/src/jit/IonBuilder.h
index 21fafd790a89..b41f8405d9d9 100644
--- a/js/src/jit/IonBuilder.h
+++ b/js/src/jit/IonBuilder.h
@@ -687,7 +687,7 @@ class IonBuilder : public MIRGenerator
     }
 
     bool isInlineBuilder() const {
-        return callerBuilder_ != NULL;
+        return callerBuilder_ != nullptr;
     }
 
   private:
diff --git a/js/src/jit/RangeAnalysis.h b/js/src/jit/RangeAnalysis.h
index bf6446df8752..cbe482e6b9f3 100644
--- a/js/src/jit/RangeAnalysis.h
+++ b/js/src/jit/RangeAnalysis.h
@@ -273,8 +273,8 @@ class Range : public TempObject {
 
     // Construct a range from the given raw values.
     Range(int32_t l, bool lb, int32_t h, bool hb, bool f, uint16_t e)
-      : symbolicLower_(NULL),
-        symbolicUpper_(NULL)
+      : symbolicLower_(nullptr),
+        symbolicUpper_(nullptr)
      {
         rawInitialize(l, lb, h, hb, f, e);
      }
diff --git a/js/src/jsalloc.h b/js/src/jsalloc.h
index 451ee3e745ef..03b6b569e18a 100644
--- a/js/src/jsalloc.h
+++ b/js/src/jsalloc.h
@@ -53,14 +53,14 @@ class TempAllocPolicy
     void *malloc_(size_t bytes) {
         void *p = js_malloc(bytes);
         if (JS_UNLIKELY(!p))
-            p = onOutOfMemory(NULL, bytes);
+            p = onOutOfMemory(nullptr, bytes);
         return p;
     }
 
     void *calloc_(size_t bytes) {
         void *p = js_calloc(bytes);
         if (JS_UNLIKELY(!p))
-            p = onOutOfMemory(NULL, bytes);
+            p = onOutOfMemory(nullptr, bytes);
         return p;
     }
 
diff --git a/js/src/jsanalyze.cpp b/js/src/jsanalyze.cpp
index d3b9b2c1626d..ebde6016c5e4 100644
--- a/js/src/jsanalyze.cpp
+++ b/js/src/jsanalyze.cpp
@@ -440,7 +440,7 @@ ScriptAnalysis::analyzeLifetimes(JSContext *cx)
     }
     unsigned savedCount = 0;
 
-    LoopAnalysis *loop = NULL;
+    LoopAnalysis *loop = nullptr;
 
     uint32_t offset = script_->length - 1;
     while (offset < script_->length) {
@@ -525,7 +525,7 @@ ScriptAnalysis::analyzeLifetimes(JSContext *cx)
                     setOOM(cx);
                     return;
                 }
-                var.saved = NULL;
+                var.saved = nullptr;
                 saved[i--] = saved[--savedCount];
             }
             savedCount = 0;
@@ -617,7 +617,7 @@ ScriptAnalysis::analyzeLifetimes(JSContext *cx)
                             setOOM(cx);
                             return;
                         }
-                        var.saved = NULL;
+                        var.saved = nullptr;
                         saved[i--] = saved[--savedCount];
                     } else if (loop && !var.savedEnd) {
                         /*
@@ -680,7 +680,7 @@ ScriptAnalysis::addVariable(JSContext *cx, LifetimeVariable &var, unsigned offse
             setOOM(cx);
             return;
         }
-        var.saved = NULL;
+        var.saved = nullptr;
     }
 }
 
@@ -730,7 +730,7 @@ ScriptAnalysis::killVariable(JSContext *cx, LifetimeVariable &var, unsigned offs
     } else {
         var.saved = var.lifetime;
         var.savedEnd = 0;
-        var.lifetime = NULL;
+        var.lifetime = nullptr;
 
         saved[savedCount++] = &var;
     }
@@ -1510,7 +1510,7 @@ ScriptAnalysis::freezeNewValues(JSContext *cx, uint32_t offset)
     Bytecode &code = getCode(offset);
 
     Vector<SlotValue> *pending = code.pendingValues;
-    code.pendingValues = NULL;
+    code.pendingValues = nullptr;
 
     unsigned count = pending->length();
     if (count == 0) {
diff --git a/js/src/jsanalyze.h b/js/src/jsanalyze.h
index 6ff82c6421d2..bc6e6efa2c28 100644
--- a/js/src/jsanalyze.h
+++ b/js/src/jsanalyze.h
@@ -336,7 +336,7 @@ struct LifetimeVariable
                 return segment;
             segment = segment->next;
         }
-        return NULL;
+        return nullptr;
     }
 
     /*
diff --git a/js/src/jsapi.cpp b/js/src/jsapi.cpp
index 7fdbd811890b..abd4238305a0 100644
--- a/js/src/jsapi.cpp
+++ b/js/src/jsapi.cpp
@@ -230,7 +230,8 @@ JS_ConvertArgumentsVA(JSContext *cx, unsigned argc, jsval *argv, const char *for
                     JS_snprintf(numBuf, sizeof numBuf, "%u", argc);
                     JSAutoByteString funNameBytes;
                     if (const char *name = GetFunctionNameBytes(cx, fun, &funNameBytes)) {
-                        JS_ReportErrorNumber(cx, js_GetErrorMessage, NULL, JSMSG_MORE_ARGS_NEEDED,
+                        JS_ReportErrorNumber(cx, js_GetErrorMessage, nullptr,
+                                             JSMSG_MORE_ARGS_NEEDED,
                                              name, numBuf, (argc == 1) ? "" : "s");
                     }
                 }
@@ -309,7 +310,7 @@ JS_ConvertArgumentsVA(JSContext *cx, unsigned argc, jsval *argv, const char *for
           case '*':
             break;
           default:
-            JS_ReportErrorNumber(cx, js_GetErrorMessage, NULL, JSMSG_BAD_CHAR, format);
+            JS_ReportErrorNumber(cx, js_GetErrorMessage, nullptr, JSMSG_BAD_CHAR, format);
             return false;
         }
         sp++;
@@ -346,11 +347,11 @@ JS_ConvertValue(JSContext *cx, HandleValue value, JSType type, MutableHandleValu
       case JSTYPE_FUNCTION:
         vp.set(value);
         obj = ReportIfNotFunction(cx, vp);
-        ok = (obj != NULL);
+        ok = (obj != nullptr);
         break;
       case JSTYPE_STRING:
         str = ToString<CanGC>(cx, value);
-        ok = (str != NULL);
+        ok = (str != nullptr);
         if (ok)
             vp.setString(str);
         break;
@@ -365,7 +366,7 @@ JS_ConvertValue(JSContext *cx, HandleValue value, JSType type, MutableHandleValu
       default: {
         char numBuf[12];
         JS_snprintf(numBuf, sizeof numBuf, "%d", (int)type);
-        JS_ReportErrorNumber(cx, js_GetErrorMessage, NULL, JSMSG_BAD_TYPE, numBuf);
+        JS_ReportErrorNumber(cx, js_GetErrorMessage, nullptr, JSMSG_BAD_TYPE, numBuf);
         ok = false;
         break;
       }
@@ -537,7 +538,7 @@ JS_PUBLIC_API(const char *)
 JS_GetTypeName(JSContext *cx, JSType type)
 {
     if ((unsigned)type >= (unsigned)JSTYPE_LIMIT)
-        return NULL;
+        return nullptr;
     return TypeStrings[type];
 }
 
@@ -714,11 +715,11 @@ JS_NewRuntime(uint32_t maxbytes, JSUseHelperThreads useHelperThreads)
 
     JSRuntime *rt = js_new<JSRuntime>(useHelperThreads);
     if (!rt)
-        return NULL;
+        return nullptr;
 
     if (!rt->init(maxbytes)) {
         JS_DestroyRuntime(rt);
-        return NULL;
+        return nullptr;
     }
 
     return rt;
@@ -739,7 +740,7 @@ JS_SetICUMemoryFunctions(JS_ICUAllocFn allocFn, JS_ICUReallocFn reallocFn, JS_IC
 
 #if EXPOSE_INTL_API
     UErrorCode status = U_ZERO_ERROR;
-    u_setMemoryFunctions(/* context = */ NULL, allocFn, reallocFn, freeFn, &status);
+    u_setMemoryFunctions(/* context = */ nullptr, allocFn, reallocFn, freeFn, &status);
     return U_SUCCESS(status);
 #else
     return true;
@@ -919,7 +920,7 @@ static const struct v2smap {
     {JSVERSION_DEFAULT, "1.3"},
     {JSVERSION_DEFAULT, "1.4"},
     {JSVERSION_DEFAULT, "1.5"},
-    {JSVERSION_UNKNOWN, NULL},          /* must be last, NULL is sentinel */
+    {JSVERSION_UNKNOWN, nullptr},          /* must be last, nullptr is sentinel */
 };
 
 JS_PUBLIC_API(const char *)
@@ -1382,7 +1383,7 @@ static const JSStdName standard_class_atoms[] = {
 #ifdef ENABLE_BINARYDATA
     {js_InitTypedObjectClasses,         EAGER_ATOM_AND_CLASP(Type)},
 #endif
-    {NULL,                              0, NULL}
+    {nullptr,                           0, nullptr}
 };
 
 /*
@@ -1449,7 +1450,7 @@ static const JSStdName standard_class_names[] = {
     {js_InitTypedObjectClasses,   EAGER_CLASS_ATOM(ArrayType),  &js::ArrayType::class_},
     {js_InitTypedObjectClasses,   EAGER_CLASS_ATOM(StructType), &js::StructType::class_},
 #endif
-    {NULL,                      0, NULL}
+    {nullptr,                     0, nullptr}
 };
 
 static const JSStdName object_prototype_names[] = {
@@ -1475,7 +1476,7 @@ static const JSStdName object_prototype_names[] = {
     {js_InitObjectClass,        EAGER_ATOM(lookupSetter), &JSObject::class_},
 #endif
 
-    {NULL,                      0, NULL}
+    {nullptr,                   0, nullptr}
 };
 
 #undef CLASP
@@ -1515,7 +1516,7 @@ JS_ResolveStandardClass(JSContext *cx, HandleObject obj, HandleId id, bool *reso
     }
 
     /* Try for class constructors/prototypes named by well-known atoms. */
-    stdnm = NULL;
+    stdnm = nullptr;
     for (i = 0; standard_class_atoms[i].init; i++) {
         JS_ASSERT(standard_class_atoms[i].clasp);
         atom = OFFSET_TO_NAME(rt, standard_class_atoms[i].atomOffset);
@@ -1699,7 +1700,7 @@ JS::CurrentGlobalOrNull(JSContext *cx)
     AssertHeapIsIdleOrIterating(cx);
     CHECK_REQUEST(cx);
     if (!cx->compartment())
-        return NULL;
+        return nullptr;
     return cx->global();
 }
 
@@ -1768,7 +1769,7 @@ JS_strdup(JSRuntime *rt, const char *s)
     size_t n = strlen(s) + 1;
     void *p = rt->malloc_(n);
     if (!p)
-        return NULL;
+        return nullptr;
     return static_cast<char*>(js_memcpy(p, s, n));
 }
 
@@ -1779,7 +1780,7 @@ JS_AddValueRoot(JSContext *cx, jsval *vp)
 {
     AssertHeapIsIdle(cx);
     CHECK_REQUEST(cx);
-    return AddValueRoot(cx, vp, NULL);
+    return AddValueRoot(cx, vp, nullptr);
 }
 
 JS_PUBLIC_API(bool)
@@ -1787,7 +1788,7 @@ JS_AddStringRoot(JSContext *cx, JSString **rp)
 {
     AssertHeapIsIdle(cx);
     CHECK_REQUEST(cx);
-    return AddStringRoot(cx, rp, NULL);
+    return AddStringRoot(cx, rp, nullptr);
 }
 
 JS_PUBLIC_API(bool)
@@ -1795,7 +1796,7 @@ JS_AddObjectRoot(JSContext *cx, JSObject **rp)
 {
     AssertHeapIsIdle(cx);
     CHECK_REQUEST(cx);
-    return AddObjectRoot(cx, rp, NULL);
+    return AddObjectRoot(cx, rp, nullptr);
 }
 
 JS_PUBLIC_API(bool)
@@ -1991,7 +1992,7 @@ DumpNotify(JSTracer *trc, void **thingp, JSGCTraceKind kind)
 
     node->thing = thing;
     node->kind = kind;
-    node->next = NULL;
+    node->next = nullptr;
     node->parent = dtrc->parentNode;
     js_memcpy(node->edgeName, edgeName, edgeNameSize);
 
@@ -2020,7 +2021,7 @@ DumpNode(JSDumpingTracer *dtrc, FILE* fp, JSHeapDumpNode *node)
      * chain order.
      */
     chainLimit = MAX_PARENTS_TO_PRINT;
-    prev = NULL;
+    prev = nullptr;
     for (;;) {
         following = node->parent;
         node->parent = prev;
@@ -2080,8 +2081,8 @@ JS_DumpHeap(JSRuntime *rt, FILE *fp, void* startThing, JSGCTraceKind startKind,
     dtrc.startThing = startThing;
     dtrc.thingToFind = thingToFind;
     dtrc.thingToIgnore = thingToIgnore;
-    dtrc.parentNode = NULL;
-    JSHeapDumpNode *node = NULL;
+    dtrc.parentNode = nullptr;
+    JSHeapDumpNode *node = nullptr;
     dtrc.lastNodep = &node;
     if (!startThing) {
         JS_ASSERT(startKind == JSTRACE_OBJECT);
@@ -2102,7 +2103,7 @@ JS_DumpHeap(JSRuntime *rt, FILE *fp, void* startThing, JSGCTraceKind startKind,
          * so far.
          */
         if (dtrc.ok) {
-            if (thingToFind == NULL || thingToFind == node->thing)
+            if (thingToFind == nullptr || thingToFind == node->thing)
                 dtrc.ok = DumpNode(&dtrc, fp, node);
 
             /* Descend into children. */
@@ -2110,12 +2111,12 @@ JS_DumpHeap(JSRuntime *rt, FILE *fp, void* startThing, JSGCTraceKind startKind,
                 depth < maxDepth &&
                 (thingToFind != node->thing || !thingToFindWasTraced)) {
                 dtrc.parentNode = node;
-                children = NULL;
+                children = nullptr;
                 dtrc.lastNodep = &children;
                 JS_TraceChildren(&dtrc.base, node->thing, node->kind);
                 if (thingToFind == node->thing)
                     thingToFindWasTraced = true;
-                if (children != NULL) {
+                if (children != nullptr) {
                     ++depth;
                     node = children;
                     continue;
@@ -2454,7 +2455,7 @@ JS_DefaultValue(JSContext *cx, JSObject *objArg, JSType hint, jsval *vp)
     RootedObject obj(cx, objArg);
     AssertHeapIsIdle(cx);
     CHECK_REQUEST(cx);
-    JS_ASSERT(obj != NULL);
+    JS_ASSERT(obj != nullptr);
     JS_ASSERT(hint == JSTYPE_VOID || hint == JSTYPE_STRING || hint == JSTYPE_NUMBER);
 
     RootedValue value(cx);
@@ -2583,7 +2584,7 @@ JS_GetInstancePrivate(JSContext *cx, JSObject *objArg, const JSClass *clasp, jsv
 {
     RootedObject obj(cx, objArg);
     if (!JS_InstanceOf(cx, obj, clasp, argv))
-        return NULL;
+        return nullptr;
     return obj->getPrivate();
 }
 
@@ -2637,12 +2638,12 @@ JS_GetConstructor(JSContext *cx, JSObject *protoArg)
         JSAutoResolveFlags rf(cx, 0);
 
         if (!JSObject::getProperty(cx, proto, proto, cx->names().constructor, &cval))
-            return NULL;
+            return nullptr;
     }
     if (!IsFunctionObject(cval)) {
-        JS_ReportErrorNumber(cx, js_GetErrorMessage, NULL, JSMSG_NO_CONSTRUCTOR,
+        JS_ReportErrorNumber(cx, js_GetErrorMessage, nullptr, JSMSG_NO_CONSTRUCTOR,
                              proto->getClass()->name);
-        return NULL;
+        return nullptr;
     }
     return &cval.toObject();
 }
@@ -2710,13 +2711,13 @@ JS_NewGlobalObject(JSContext *cx, const JSClass *clasp, JSPrincipals *principals
     if (options.zoneSpecifier() == JS::SystemZone)
         zone = rt->systemZone;
     else if (options.zoneSpecifier() == JS::FreshZone)
-        zone = NULL;
+        zone = nullptr;
     else
         zone = static_cast<Zone *>(options.zonePointer());
 
     JSCompartment *compartment = NewCompartment(cx, zone, principals, options);
     if (!compartment)
-        return NULL;
+        return nullptr;
 
     // Lazily create the system zone.
     if (!rt->systemZone && options.zoneSpecifier() == JS::SystemZone) {
@@ -2733,7 +2734,7 @@ JS_NewGlobalObject(JSContext *cx, const JSClass *clasp, JSPrincipals *principals
     }
 
     if (!global)
-        return NULL;
+        return nullptr;
 
     if (hookOption == JS::FireOnNewGlobalHook)
         JS_FireOnNewGlobalObject(cx, global);
@@ -3004,7 +3005,7 @@ JS_HasPropertyById(JSContext *cx, JSObject *objArg, jsid idArg, bool *foundp)
     RootedObject obj2(cx);
     RootedShape prop(cx);
     bool ok = LookupPropertyById(cx, obj, id, 0, &obj2, &prop);
-    *foundp = (prop != NULL);
+    *foundp = (prop != nullptr);
     return ok;
 }
 
@@ -3101,7 +3102,7 @@ GetterWrapper(JSPropertyOp getter)
 {
     JSPropertyOpWrapper ret;
     ret.op = getter;
-    ret.info = NULL;
+    ret.info = nullptr;
     return ret;
 }
 
@@ -3110,7 +3111,7 @@ SetterWrapper(JSStrictPropertyOp setter)
 {
     JSStrictPropertyOpWrapper ret;
     ret.op = setter;
-    ret.info = NULL;
+    ret.info = nullptr;
     return ret;
 }
 
@@ -3158,7 +3159,7 @@ DefinePropertyById(JSContext *cx, HandleObject obj, HandleId id, HandleValue val
         }
         if (setter) {
             // Root just the getter, since the setter is not yet a JSObject.
-            AutoRooterGetterSetter getRoot(cx, JSPROP_GETTER, &getter, NULL);
+            AutoRooterGetterSetter getRoot(cx, JSPROP_GETTER, &getter, nullptr);
             RootedObject global(cx, (JSObject*) &obj->global());
             JSFunction *setobj = NewFunction(cx, NullPtr(), (Native) setter, 1,
                                              zeroFlags, global, atom);
@@ -3179,10 +3180,10 @@ DefinePropertyById(JSContext *cx, HandleObject obj, HandleId id, HandleValue val
     assertSameCompartment(cx, obj, id, value,
                             (attrs & JSPROP_GETTER)
                             ? JS_FUNC_TO_DATA_PTR(JSObject *, getter)
-                            : NULL,
+                            : nullptr,
                             (attrs & JSPROP_SETTER)
                             ? JS_FUNC_TO_DATA_PTR(JSObject *, setter)
-                            : NULL);
+                            : nullptr);
 
     JSAutoResolveFlags rf(cx, 0);
     if (flags != 0 && obj->isNative()) {
@@ -3326,12 +3327,12 @@ JS_DefineObject(JSContext *cx, JSObject *objArg, const char *name, const JSClass
 
     RootedObject nobj(cx, NewObjectWithClassProto(cx, clasp, proto, obj));
     if (!nobj)
-        return NULL;
+        return nullptr;
 
-    if (!DefineProperty(cx, obj, name, ObjectValue(*nobj), GetterWrapper(NULL),
-                        SetterWrapper(NULL), attrs, 0, 0))
+    if (!DefineProperty(cx, obj, name, ObjectValue(*nobj), GetterWrapper(nullptr),
+                        SetterWrapper(nullptr), attrs, 0, 0))
     {
-        return NULL;
+        return nullptr;
     }
 
     return nobj;
@@ -3346,8 +3347,8 @@ JS_DefineConstDoubles(JSContext *cx, JSObject *objArg, const JSConstDoubleSpec *
 
     AssertHeapIsIdle(cx);
     CHECK_REQUEST(cx);
-    JSPropertyOpWrapper noget = GetterWrapper(NULL);
-    JSStrictPropertyOpWrapper noset = SetterWrapper(NULL);
+    JSPropertyOpWrapper noget = GetterWrapper(nullptr);
+    JSStrictPropertyOpWrapper noset = SetterWrapper(nullptr);
     for (ok = true; cds->name; cds++) {
         Value value = DoubleValue(cds->dval);
         attrs = cds->flags;
@@ -3410,8 +3411,8 @@ GetPropertyDescriptorById(JSContext *cx, HandleObject obj, HandleId id, unsigned
         }
         if (!JSObject::getGenericAttributes(cx, obj2, id, &desc.attributesRef()))
             return false;
-        JS_ASSERT(desc.getter() == NULL);
-        JS_ASSERT(desc.setter() == NULL);
+        JS_ASSERT(desc.getter() == nullptr);
+        JS_ASSERT(desc.setter() == nullptr);
         JS_ASSERT(desc.value().isUndefined());
     }
     return true;
@@ -3690,7 +3691,7 @@ LastConfigurableShape(JSObject *obj)
         if (shape->configurable())
             return shape;
     }
-    return NULL;
+    return nullptr;
 }
 
 JS_PUBLIC_API(void)
@@ -3755,7 +3756,7 @@ JS_Enumerate(JSContext *cx, JSObject *objArg)
     AutoIdVector props(cx);
     JSIdArray *ida;
     if (!GetPropertyNames(cx, obj, JSITER_OWNONLY, &props) || !VectorToIdArray(cx, props, &ida))
-        return NULL;
+        return nullptr;
     return ida;
 }
 
@@ -3816,10 +3817,10 @@ static const Class prop_iter_class = {
     JS_ResolveStub,
     JS_ConvertStub,
     prop_iter_finalize,
-    NULL,           /* checkAccess */
-    NULL,           /* call        */
-    NULL,           /* hasInstance */
-    NULL,           /* construct   */
+    nullptr,        /* checkAccess */
+    nullptr,        /* call        */
+    nullptr,        /* hasInstance */
+    nullptr,        /* construct   */
     prop_iter_trace
 };
 
@@ -3832,9 +3833,9 @@ JS_NewPropertyIterator(JSContext *cx, JSObject *objArg)
     CHECK_REQUEST(cx);
     assertSameCompartment(cx, obj);
 
-    RootedObject iterobj(cx, NewObjectWithClassProto(cx, &prop_iter_class, NULL, obj));
+    RootedObject iterobj(cx, NewObjectWithClassProto(cx, &prop_iter_class, nullptr, obj));
     if (!iterobj)
-        return NULL;
+        return nullptr;
 
     int index;
     if (obj->isNative()) {
@@ -3845,7 +3846,7 @@ JS_NewPropertyIterator(JSContext *cx, JSObject *objArg)
         /* Non-native case: enumerate a JSIdArray and keep it via private. */
         JSIdArray *ida = JS_Enumerate(cx, obj);
         if (!ida)
-            return NULL;
+            return nullptr;
         iterobj->setPrivate((void *)ida);
         index = ida->length;
     }
@@ -4003,7 +4004,7 @@ JS_SetSecurityCallbacks(JSRuntime *rt, const JSSecurityCallbacks *scb)
 JS_PUBLIC_API(const JSSecurityCallbacks *)
 JS_GetSecurityCallbacks(JSRuntime *rt)
 {
-    return (rt->securityCallbacks != &NullSecurityCallbacks) ? rt->securityCallbacks : NULL;
+    return (rt->securityCallbacks != &NullSecurityCallbacks) ? rt->securityCallbacks : nullptr;
 }
 
 JS_PUBLIC_API(void)
@@ -4035,7 +4036,7 @@ JS_NewFunction(JSContext *cx, JSNative native, unsigned nargs, unsigned flags,
     if (name) {
         atom = Atomize(cx, name, strlen(name));
         if (!atom)
-            return NULL;
+            return nullptr;
     }
 
     JSFunction::Flags funFlags = JSAPIToJSFunctionFlags(flags);
@@ -4093,7 +4094,7 @@ JS_CloneFunctionObject(JSContext *cx, JSObject *funobjArg, JSObject *parentArg)
     if (!funobj->is<JSFunction>()) {
         AutoCompartment ac(cx, funobj);
         ReportIsNotFunction(cx, ObjectValue(*funobj));
-        return NULL;
+        return nullptr;
     }
 
     /*
@@ -4104,23 +4105,23 @@ JS_CloneFunctionObject(JSContext *cx, JSObject *funobjArg, JSObject *parentArg)
     if (fun->isInterpretedLazy()) {
         AutoCompartment ac(cx, funobj);
         if (!fun->getOrCreateScript(cx))
-            return NULL;
+            return nullptr;
     }
     if (fun->isInterpreted() && (fun->nonLazyScript()->enclosingStaticScope() ||
         (fun->nonLazyScript()->compileAndGo && !parent->is<GlobalObject>())))
     {
-        JS_ReportErrorNumber(cx, js_GetErrorMessage, NULL, JSMSG_BAD_CLONE_FUNOBJ_SCOPE);
-        return NULL;
+        JS_ReportErrorNumber(cx, js_GetErrorMessage, nullptr, JSMSG_BAD_CLONE_FUNOBJ_SCOPE);
+        return nullptr;
     }
 
     if (fun->isBoundFunction()) {
-        JS_ReportErrorNumber(cx, js_GetErrorMessage, NULL, JSMSG_CANT_CLONE_OBJECT);
-        return NULL;
+        JS_ReportErrorNumber(cx, js_GetErrorMessage, nullptr, JSMSG_CANT_CLONE_OBJECT);
+        return nullptr;
     }
 
     if (fun->isNative() && IsAsmJSModuleNative(fun->native())) {
-        JS_ReportErrorNumber(cx, js_GetErrorMessage, NULL, JSMSG_CANT_CLONE_OBJECT);
-        return NULL;
+        JS_ReportErrorNumber(cx, js_GetErrorMessage, nullptr, JSMSG_CANT_CLONE_OBJECT);
+        return nullptr;
     }
 
     return CloneFunctionObject(cx, fun, parent, fun->getAllocKind());
@@ -4182,7 +4183,7 @@ JS_BindCallable(JSContext *cx, JSObject *targetArg, JSObject *newThis)
 {
     RootedObject target(cx, targetArg);
     RootedValue thisArg(cx, ObjectValue(*newThis));
-    return js_fun_bind(cx, target, thisArg, NULL, 0);
+    return js_fun_bind(cx, target, thisArg, nullptr, 0);
 }
 
 static bool
@@ -4268,7 +4269,7 @@ JS_DefineFunctions(JSContext *cx, JSObject *objArg, const JSFunctionSpec *fs)
 
         /*
          * Delay cloning self-hosted functions until they are called. This is
-         * achieved by passing DefineFunction a NULL JSNative which
+         * achieved by passing DefineFunction a nullptr JSNative which
          * produces an interpreted JSFunction where !hasScript. Interpreted
          * call paths then call InitializeLazyFunctionScript if !hasScript.
          */
@@ -4291,7 +4292,7 @@ JS_DefineFunctions(JSContext *cx, JSObject *objArg, const JSFunctionSpec *fs)
             RootedValue funVal(cx);
             if (!cx->global()->getSelfHostedFunction(cx, shName, atom, fs->nargs, &funVal))
                 return false;
-            if (!JSObject::defineGeneric(cx, obj, id, funVal, NULL, NULL, flags))
+            if (!JSObject::defineGeneric(cx, obj, id, funVal, nullptr, nullptr, flags))
                 return false;
         } else {
             JSFunction *fun = DefineFunction(cx, obj, id, fs->call.op, fs->nargs, flags);
@@ -4315,7 +4316,7 @@ JS_DefineFunction(JSContext *cx, JSObject *objArg, const char *name, JSNative ca
     assertSameCompartment(cx, obj);
     JSAtom *atom = Atomize(cx, name, strlen(name));
     if (!atom)
-        return NULL;
+        return nullptr;
     Rooted<jsid> id(cx, AtomToId(atom));
     return DefineFunction(cx, obj, id, call, nargs, attrs);
 }
@@ -4332,7 +4333,7 @@ JS_DefineUCFunction(JSContext *cx, JSObject *objArg,
     assertSameCompartment(cx, obj);
     JSAtom *atom = AtomizeChars<CanGC>(cx, name, AUTO_NAMELEN(name, namelen));
     if (!atom)
-        return NULL;
+        return nullptr;
     Rooted<jsid> id(cx, AtomToId(atom));
     return DefineFunction(cx, obj, id, call, nargs, attrs);
 }
@@ -4419,7 +4420,7 @@ class AutoFile
     FILE *fp_;
   public:
     AutoFile()
-      : fp_(NULL)
+      : fp_(nullptr)
     {}
     ~AutoFile()
     {
@@ -4438,7 +4439,7 @@ class AutoFile
 } /* anonymous namespace */
 
 /*
- * Open a source file for reading. Supports "-" and NULL to mean stdin. The
+ * Open a source file for reading. Supports "-" and nullptr to mean stdin. The
  * return value must be fclosed unless it is stdin.
  */
 bool
@@ -4449,7 +4450,7 @@ AutoFile::open(JSContext *cx, const char *filename)
     } else {
         fp_ = fopen(filename, "r");
         if (!fp_) {
-            JS_ReportErrorNumber(cx, js_GetErrorMessage, NULL, JSMSG_CANT_OPEN,
+            JS_ReportErrorNumber(cx, js_GetErrorMessage, nullptr, JSMSG_CANT_OPEN,
                                  filename, "No such file or directory");
             return false;
         }
@@ -4459,13 +4460,13 @@ AutoFile::open(JSContext *cx, const char *filename)
 
 
 JS::CompileOptions::CompileOptions(JSContext *cx, JSVersion version)
-    : principals_(NULL),
-      originPrincipals_(NULL),
+    : principals_(nullptr),
+      originPrincipals_(nullptr),
       version(version != JSVERSION_UNKNOWN ? version : cx->findVersion()),
       versionSet(false),
       utf8(false),
-      filename(NULL),
-      sourceMapURL(NULL),
+      filename(nullptr),
+      sourceMapURL(nullptr),
       lineno(1),
       column(0),
       element(NullPtr()),
@@ -4512,7 +4513,7 @@ JS::Compile(JSContext *cx, HandleObject obj, CompileOptions options,
     else
         chars = InflateString(cx, bytes, &length);
     if (!chars)
-        return NULL;
+        return nullptr;
 
     JSScript *script = Compile(cx, obj, options, chars, length);
     js_free(chars);
@@ -4524,7 +4525,7 @@ JS::Compile(JSContext *cx, HandleObject obj, CompileOptions options, FILE *fp)
 {
     FileContents buffer(cx);
     if (!ReadCompleteFile(cx, fp, buffer))
-        return NULL;
+        return nullptr;
 
     JSScript *script = Compile(cx, obj, options, buffer.begin(), buffer.length());
     return script;
@@ -4535,7 +4536,7 @@ JS::Compile(JSContext *cx, HandleObject obj, CompileOptions options, const char
 {
     AutoFile file;
     if (!file.open(cx, filename))
-        return NULL;
+        return nullptr;
     options = options.setFileAndLine(filename, 1);
     JSScript *script = Compile(cx, obj, options, file.fp());
     return script;
@@ -4568,7 +4569,7 @@ JS::CanCompileOffThread(JSContext *cx, const CompileOptions &options)
         "chrome://browser/content/newtab/newTab.js",
         "chrome://browser/content/places/browserPlacesViews.js",
 #endif
-        NULL
+        nullptr
     };
 
     const char *filename = options.filename;
@@ -4682,8 +4683,8 @@ JS_BufferIsCompilableUnit(JSContext *cx, JSObject *objArg, const char *utf8, siz
         options.setCompileAndGo(false);
         Parser<frontend::FullParseHandler> parser(cx, &cx->tempLifoAlloc(),
                                                   options, chars, length,
-                                                  /* foldConstants = */ true, NULL, NULL);
-        older = JS_SetErrorReporter(cx, NULL);
+                                                  /* foldConstants = */ true, nullptr, nullptr);
+        older = JS_SetErrorReporter(cx, nullptr);
         if (!parser.parse(obj) && parser.isUnexpectedEOF()) {
             /*
              * We ran into an error. If it was because we ran out of
@@ -4722,29 +4723,29 @@ JS::CompileFunction(JSContext *cx, HandleObject obj, CompileOptions options,
     if (name) {
         funAtom = Atomize(cx, name, strlen(name));
         if (!funAtom)
-            return NULL;
+            return nullptr;
     }
 
     AutoNameVector formals(cx);
     for (unsigned i = 0; i < nargs; i++) {
         RootedAtom argAtom(cx, Atomize(cx, argnames[i], strlen(argnames[i])));
         if (!argAtom || !formals.append(argAtom->asPropertyName()))
-            return NULL;
+            return nullptr;
     }
 
-    RootedFunction fun(cx, NewFunction(cx, NullPtr(), NULL, 0, JSFunction::INTERPRETED, obj,
+    RootedFunction fun(cx, NewFunction(cx, NullPtr(), nullptr, 0, JSFunction::INTERPRETED, obj,
                                        funAtom, JSFunction::FinalizeKind, TenuredObject));
     if (!fun)
-        return NULL;
+        return nullptr;
 
     if (!frontend::CompileFunctionBody(cx, &fun, options, formals, chars, length))
-        return NULL;
+        return nullptr;
 
     if (obj && funAtom) {
         Rooted<jsid> id(cx, AtomToId(funAtom));
         RootedValue value(cx, ObjectValue(*fun));
-        if (!JSObject::defineGeneric(cx, obj, id, value, NULL, NULL, JSPROP_ENUMERATE))
-            return NULL;
+        if (!JSObject::defineGeneric(cx, obj, id, value, nullptr, nullptr, JSPROP_ENUMERATE))
+            return nullptr;
     }
 
     return fun;
@@ -4761,7 +4762,7 @@ JS::CompileFunction(JSContext *cx, HandleObject obj, CompileOptions options,
     else
         chars = InflateString(cx, bytes, &length);
     if (!chars)
-        return NULL;
+        return nullptr;
 
     JSFunction *fun = CompileFunction(cx, obj, options, name, nargs, argnames, chars, length);
     js_free(chars);
@@ -4822,7 +4823,7 @@ JS_DecompileScript(JSContext *cx, JSScript *scriptArg, const char *name, unsigne
         return JS_DecompileFunction(cx, fun, indent);
     bool haveSource = script->scriptSource()->hasSourceData();
     if (!haveSource && !JSScript::loadSource(cx, script->scriptSource(), &haveSource))
-        return NULL;
+        return nullptr;
     return haveSource ? script->sourceData(cx) : js_NewStringCopyZ<CanGC>(cx, "[no source]");
 }
 
@@ -4908,7 +4909,7 @@ JS::Evaluate(JSContext *cx, HandleObject obj, CompileOptions options,
     SourceCompressionTask sct(cx);
     RootedScript script(cx, frontend::CompileScript(cx, &cx->tempLifoAlloc(),
                                                     obj, NullPtr(), options,
-                                                    chars, length, NULL, 0, &sct));
+                                                    chars, length, nullptr, 0, &sct));
     if (!script)
         return false;
 
@@ -4924,7 +4925,7 @@ JS::Evaluate(JSContext *cx, HandleObject obj, CompileOptions options,
     // to clear out this analysis data before anything happens to inhibit the
     // flushing of this memory (such as setting requestAnimationFrame).
     if (script->length > LARGE_SCRIPT_LENGTH) {
-        script = NULL;
+        script = nullptr;
         PrepareZoneForGC(cx->zone());
         GC(cx->runtime(), GC_NORMAL, gcreason::FINISH_LARGE_EVALUTE);
     }
@@ -5154,14 +5155,14 @@ JS_New(JSContext *cx, JSObject *ctorArg, unsigned argc, jsval *argv)
     // among other details. InvokeConstructor does the hard work.
     InvokeArgs args(cx);
     if (!args.init(argc))
-        return NULL;
+        return nullptr;
 
     args.setCallee(ObjectValue(*ctor));
     args.setThis(NullValue());
     PodCopy(args.array(), argv, argc);
 
     if (!InvokeConstructor(cx, args))
-        return NULL;
+        return nullptr;
 
     if (!args.rval().isObject()) {
         /*
@@ -5170,10 +5171,10 @@ JS_New(JSContext *cx, JSObject *ctorArg, unsigned argc, jsval *argv)
          */
         JSAutoByteString bytes;
         if (js_ValueToPrintable(cx, args.rval(), &bytes)) {
-            JS_ReportErrorNumber(cx, js_GetErrorMessage, NULL, JSMSG_BAD_NEW_RESULT,
+            JS_ReportErrorNumber(cx, js_GetErrorMessage, nullptr, JSMSG_BAD_NEW_RESULT,
                                  bytes.ptr());
         }
-        return NULL;
+        return nullptr;
     }
 
     return &args.rval().toObject();
@@ -5258,7 +5259,7 @@ JS_NewStringCopyZ(JSContext *cx, const char *s)
     n = strlen(s);
     js = InflateString(cx, s, &n);
     if (!js)
-        return NULL;
+        return nullptr;
     str = js_NewString<CanGC>(cx, js, n);
     if (!str)
         js_free(js);
@@ -5379,7 +5380,7 @@ JS_GetStringCharsZAndLength(JSContext *cx, JSString *str, size_t *plength)
     CHECK_REQUEST(cx);
     JSFlatString *flat = str->ensureFlat(cx);
     if (!flat)
-        return NULL;
+        return nullptr;
     *plength = flat->length();
     return flat->chars();
 }
@@ -5393,7 +5394,7 @@ JS_GetStringCharsAndLength(JSContext *cx, JSString *str, size_t *plength)
     assertSameCompartment(cx, str);
     JSLinearString *linear = str->ensureLinear(cx);
     if (!linear)
-        return NULL;
+        return nullptr;
     *plength = linear->length();
     return linear->chars();
 }
@@ -5402,9 +5403,9 @@ JS_PUBLIC_API(const jschar *)
 JS_GetInternedStringChars(JSString *str)
 {
     JS_ASSERT(str->isAtom());
-    JSFlatString *flat = str->ensureFlat(NULL);
+    JSFlatString *flat = str->ensureFlat(nullptr);
     if (!flat)
-        return NULL;
+        return nullptr;
     return flat->chars();
 }
 
@@ -5413,9 +5414,9 @@ JS_GetInternedStringCharsAndLength(JSString *str, size_t *plength)
 {
     JS_ASSERT(str->isAtom());
     JS_ASSERT(plength);
-    JSFlatString *flat = str->ensureFlat(NULL);
+    JSFlatString *flat = str->ensureFlat(nullptr);
     if (!flat)
-        return NULL;
+        return nullptr;
     *plength = flat->length();
     return flat->chars();
 }
@@ -5428,7 +5429,7 @@ JS_FlattenString(JSContext *cx, JSString *str)
     assertSameCompartment(cx, str);
     JSFlatString *flat = str->ensureFlat(cx);
     if (!flat)
-        return NULL;
+        return nullptr;
     return flat;
 }
 
@@ -5485,7 +5486,7 @@ JS_PutEscapedString(JSContext *cx, char *buffer, size_t size, JSString *str, cha
 JS_PUBLIC_API(bool)
 JS_FileEscapedString(FILE *fp, JSString *str, char quote)
 {
-    JSLinearString *linearStr = str->ensureLinear(NULL);
+    JSLinearString *linearStr = str->ensureLinear(nullptr);
     return linearStr && FileEscapedString(fp, linearStr, quote);
 }
 
@@ -5522,7 +5523,7 @@ JS_DecodeBytes(JSContext *cx, const char *src, size_t srclen, jschar *dst, size_
         InflateStringToBuffer(src, dstlen, dst);
 
         AutoSuppressGC suppress(cx);
-        JS_ReportErrorNumber(cx, js_GetErrorMessage, NULL, JSMSG_BUFFER_TOO_SMALL);
+        JS_ReportErrorNumber(cx, js_GetErrorMessage, nullptr, JSMSG_BUFFER_TOO_SMALL);
         return false;
     }
 
@@ -5539,7 +5540,7 @@ JS_EncodeString(JSContext *cx, JSString *str)
 
     JSLinearString *linear = str->ensureLinear(cx);
     if (!linear)
-        return NULL;
+        return nullptr;
 
     return LossyTwoByteCharsToNewLatin1CharsZ(cx, linear->range()).c_str();
 }
@@ -5552,7 +5553,7 @@ JS_EncodeStringToUTF8(JSContext *cx, JSString *str)
 
     JSLinearString *linear = str->ensureLinear(cx);
     if (!linear)
-        return NULL;
+        return nullptr;
 
     return TwoByteCharsToNewUTF8CharsZ(cx, linear->range()).c_str();
 }
@@ -5581,10 +5582,10 @@ JS_EncodeStringToBuffer(JSContext *cx, JSString *str, char *buffer, size_t lengt
      * error.
      */
     size_t writtenLength = length;
-    const jschar *chars = str->getChars(NULL);
+    const jschar *chars = str->getChars(nullptr);
     if (!chars)
         return size_t(-1);
-    if (DeflateStringToBuffer(NULL, chars, str->length(), buffer, &writtenLength)) {
+    if (DeflateStringToBuffer(nullptr, chars, str->length(), buffer, &writtenLength)) {
         JS_ASSERT(writtenLength <= length);
         return writtenLength;
     }
@@ -5808,11 +5809,11 @@ JS_NewRegExpObject(JSContext *cx, HandleObject obj, char *bytes, size_t length,
     CHECK_REQUEST(cx);
     jschar *chars = InflateString(cx, bytes, &length);
     if (!chars)
-        return NULL;
+        return nullptr;
 
     RegExpStatics *res = obj->as<GlobalObject>().getRegExpStatics();
     RegExpObject *reobj = RegExpObject::create(cx, res, chars, length,
-                                               RegExpFlag(flags), NULL);
+                                               RegExpFlag(flags), nullptr);
     js_free(chars);
     return reobj;
 }
@@ -5825,7 +5826,7 @@ JS_NewUCRegExpObject(JSContext *cx, HandleObject obj, jschar *chars, size_t leng
     CHECK_REQUEST(cx);
     RegExpStatics *res = obj->as<GlobalObject>().getRegExpStatics();
     return RegExpObject::create(cx, res, chars, length,
-                                RegExpFlag(flags), NULL);
+                                RegExpFlag(flags), nullptr);
 }
 
 JS_PUBLIC_API(void)
@@ -5868,9 +5869,9 @@ JS_NewRegExpObjectNoStatics(JSContext *cx, char *bytes, size_t length, unsigned
     CHECK_REQUEST(cx);
     jschar *chars = InflateString(cx, bytes, &length);
     if (!chars)
-        return NULL;
+        return nullptr;
     RegExpObject *reobj = RegExpObject::createNoStatics(cx, chars, length,
-                                                        RegExpFlag(flags), NULL);
+                                                        RegExpFlag(flags), nullptr);
     js_free(chars);
     return reobj;
 }
@@ -5881,7 +5882,7 @@ JS_NewUCRegExpObjectNoStatics(JSContext *cx, jschar *chars, size_t length, unsig
     AssertHeapIsIdle(cx);
     CHECK_REQUEST(cx);
     return RegExpObject::createNoStatics(cx, chars, length,
-                                         RegExpFlag(flags), NULL);
+                                         RegExpFlag(flags), nullptr);
 }
 
 JS_PUBLIC_API(bool)
@@ -5891,8 +5892,8 @@ JS_ExecuteRegExpNoStatics(JSContext *cx, HandleObject obj, jschar *chars, size_t
     AssertHeapIsIdle(cx);
     CHECK_REQUEST(cx);
 
-    return ExecuteRegExpLegacy(cx, NULL, obj->as<RegExpObject>(), NullPtr(), chars, length, indexp,
-                               test, rval);
+    return ExecuteRegExpLegacy(cx, nullptr, obj->as<RegExpObject>(), NullPtr(), chars, length,
+                               indexp, test, rval);
 }
 
 JS_PUBLIC_API(bool)
@@ -6064,7 +6065,7 @@ JS_ThrowReportedError(JSContext *cx, const char *message,
 {
     AssertHeapIsIdle(cx);
     return JS_IsRunning(cx) &&
-           js_ErrorToException(cx, message, reportp, NULL, NULL);
+           js_ErrorToException(cx, message, reportp, nullptr, nullptr);
 }
 
 JS_PUBLIC_API(bool)
@@ -6207,7 +6208,7 @@ JS_IsIdentifier(JSContext *cx, HandleString str, bool *isIdentifier)
 JS_PUBLIC_API(bool)
 JS_DescribeScriptedCaller(JSContext *cx, MutableHandleScript script, unsigned *lineno)
 {
-    script.set(NULL);
+    script.set(nullptr);
     if (lineno)
         *lineno = 0;
 
@@ -6279,7 +6280,7 @@ JS_EncodeScript(JSContext *cx, HandleScript scriptArg, uint32_t *lengthp)
     XDREncoder encoder(cx);
     RootedScript script(cx, scriptArg);
     if (!encoder.codeScript(&script))
-        return NULL;
+        return nullptr;
     return encoder.forgetData(lengthp);
 }
 
@@ -6289,7 +6290,7 @@ JS_EncodeInterpretedFunction(JSContext *cx, HandleObject funobjArg, uint32_t *le
     XDREncoder encoder(cx);
     RootedObject funobj(cx, funobjArg);
     if (!encoder.codeFunction(&funobj))
-        return NULL;
+        return nullptr;
     return encoder.forgetData(lengthp);
 }
 
@@ -6300,7 +6301,7 @@ JS_DecodeScript(JSContext *cx, const void *data, uint32_t length,
     XDRDecoder decoder(cx, data, length, principals, originPrincipals);
     RootedScript script(cx);
     if (!decoder.codeScript(&script))
-        return NULL;
+        return nullptr;
     return script;
 }
 
@@ -6311,7 +6312,7 @@ JS_DecodeInterpretedFunction(JSContext *cx, const void *data, uint32_t length,
     XDRDecoder decoder(cx, data, length, principals, originPrincipals);
     RootedObject funobj(cx);
     if (!decoder.codeFunction(&funobj))
-        return NULL;
+        return nullptr;
     return funobj;
 }
 
@@ -6340,7 +6341,7 @@ JSAutoByteString::encodeLatin1(ExclusiveContext *cx, JSString *str)
 {
     JSLinearString *linear = str->ensureLinear(cx);
     if (!linear)
-        return NULL;
+        return nullptr;
 
     mBytes = LossyTwoByteCharsToNewLatin1CharsZ(cx, linear->range()).c_str();
     return mBytes;
diff --git a/js/src/jsapi.h b/js/src/jsapi.h
index 9a5d09454a48..efc93220cd47 100644
--- a/js/src/jsapi.h
+++ b/js/src/jsapi.h
@@ -150,7 +150,7 @@ class JS_PUBLIC_API(AutoGCRooter) {
 
 class AutoStringRooter : private AutoGCRooter {
   public:
-    AutoStringRooter(JSContext *cx, JSString *str = NULL
+    AutoStringRooter(JSContext *cx, JSString *str = nullptr
                      MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
       : AutoGCRooter(cx, STRING), str_(str)
     {
@@ -802,10 +802,10 @@ typedef bool
  * Callback used to ask the embedding for the cross compartment wrapper handler
  * that implements the desired prolicy for this kind of object in the
  * destination compartment. |obj| is the object to be wrapped. If |existing| is
- * non-NULL, it will point to an existing wrapper object that should be re-used
- * if possible. |existing| is guaranteed to be a cross-compartment wrapper with
- * a lazily-defined prototype and the correct global. It is guaranteed not to
- * wrap a function.
+ * non-nullptr, it will point to an existing wrapper object that should be
+ * re-used if possible. |existing| is guaranteed to be a cross-compartment
+ * wrapper with a lazily-defined prototype and the correct global. It is
+ * guaranteed not to wrap a function.
  */
 typedef JSObject *
 (* JSWrapObjectCallback)(JSContext *cx, JS::Handle<JSObject*> existing, JS::Handle<JSObject*> obj,
@@ -1329,7 +1329,7 @@ JS_DestroyRuntime(JSRuntime *rt);
 
 // These are equivalent to ICU's |UMemAllocFn|, |UMemReallocFn|, and
 // |UMemFreeFn| types.  The first argument (called |context| in the ICU docs)
-// will always be NULL, and should be ignored.
+// will always be nullptr, and should be ignored.
 typedef void *(*JS_ICUAllocFn)(const void *, size_t size);
 typedef void *(*JS_ICUReallocFn)(const void *, void *p, size_t size);
 typedef void (*JS_ICUFreeFn)(const void *, void *p);
@@ -1589,7 +1589,7 @@ extern JS_PUBLIC_API(bool)
 JS_RefreshCrossCompartmentWrappers(JSContext *cx, JSObject *ob);
 
 /*
- * At any time, a JSContext has a current (possibly-NULL) compartment.
+ * At any time, a JSContext has a current (possibly-nullptr) compartment.
  * Compartments are described in:
  *
  *   developer.mozilla.org/en-US/docs/SpiderMonkey/SpiderMonkey_compartments
@@ -1633,7 +1633,7 @@ class JS_PUBLIC_API(JSAutoCompartment)
     ~JSAutoCompartment();
 };
 
-/* NB: This API is infallible; a NULL return value does not indicate error. */
+/* NB: This API is infallible; a nullptr return value does not indicate error. */
 extern JS_PUBLIC_API(JSCompartment *)
 JS_EnterCompartment(JSContext *cx, JSObject *target);
 
@@ -1718,8 +1718,8 @@ extern JS_PUBLIC_API(bool)
 JS_IsGlobalObject(JSObject *obj);
 
 /*
- * May return NULL, if |c| never had a global (e.g. the atoms compartment), or
- * if |c|'s global has been collected.
+ * May return nullptr, if |c| never had a global (e.g. the atoms compartment),
+ * or if |c|'s global has been collected.
  */
 extern JS_PUBLIC_API(JSObject *)
 JS_GetGlobalForCompartmentOrNull(JSContext *cx, JSCompartment *c);
@@ -1767,7 +1767,7 @@ typedef char *
 
 /*
  * Set of function pointers that ctypes can use for various internal functions.
- * See JS_SetCTypesCallbacks below. Providing NULL for a function is safe,
+ * See JS_SetCTypesCallbacks below. Providing nullptr for a function is safe,
  * and will result in the applicable ctypes functionality not being available.
  */
 struct JSCTypesCallbacks {
@@ -1805,7 +1805,7 @@ JS_realloc(JSContext *cx, void *p, size_t nbytes);
 /*
  * A wrapper for js_free(p) that may delay js_free(p) invocation as a
  * performance optimization.
- * cx may be NULL.
+ * cx may be nullptr.
  */
 extern JS_PUBLIC_API(void)
 JS_free(JSContext *cx, void *p);
@@ -2153,8 +2153,8 @@ extern JS_PUBLIC_API(bool)
 JS_IsExternalString(JSString *str);
 
 /*
- * Return the 'closure' arg passed to JS_NewExternalStringWithClosure or NULL
- * if the external string was created via JS_NewExternalString.
+ * Return the 'closure' arg passed to JS_NewExternalStringWithClosure or
+ * nullptr if the external string was created via JS_NewExternalString.
  */
 extern JS_PUBLIC_API(const JSStringFinalizer *)
 JS_GetExternalStringFinalizer(JSString *str);
@@ -2221,7 +2221,7 @@ class AutoIdArray : private AutoGCRooter
 
     JSIdArray *steal() {
         JSIdArray *copy = idArray;
-        idArray = NULL;
+        idArray = nullptr;
         return copy;
     }
 
@@ -2318,8 +2318,8 @@ typedef struct JSNativeWrapper {
  * Macro static initializers which make it easy to pass no JSJitInfo as part of a
  * JSPropertySpec or JSFunctionSpec.
  */
-#define JSOP_WRAPPER(op) {op, NULL}
-#define JSOP_NULLWRAPPER JSOP_WRAPPER(NULL)
+#define JSOP_WRAPPER(op) {op, nullptr}
+#define JSOP_NULLWRAPPER JSOP_WRAPPER(nullptr)
 
 /*
  * To define an array element rather than a named property member, cast the
@@ -2387,7 +2387,7 @@ struct JSFunctionSpec {
  * Terminating sentinel initializer to put at the end of a JSFunctionSpec array
  * that's passed to JS_DefineFunctions or JS_InitClass.
  */
-#define JS_FS_END JS_FS(NULL,NULL,0,0)
+#define JS_FS_END JS_FS(nullptr,nullptr,0,0)
 
 /*
  * Initializer macros for a JSFunctionSpec array element. JS_FN (whose name pays
@@ -2655,8 +2655,8 @@ struct JSPropertyDescriptor {
     JSStrictPropertyOp setter;
     JS::Value          value;
 
-    JSPropertyDescriptor() : obj(NULL), attrs(0), shortid(0), getter(NULL),
-                             setter(NULL), value(JSVAL_VOID)
+    JSPropertyDescriptor() : obj(nullptr), attrs(0), shortid(0), getter(nullptr),
+                             setter(nullptr), value(JSVAL_VOID)
     {}
 
     void trace(JSTracer *trc);
@@ -2712,11 +2712,11 @@ class MutablePropertyDescriptorOperations : public PropertyDescriptorOperations<
   public:
 
     void clear() {
-        object().set(NULL);
+        object().set(nullptr);
         setAttributes(0);
         setShortId(0);
-        setGetter(NULL);
-        setSetter(NULL);
+        setGetter(nullptr);
+        setSetter(nullptr);
         value().setUndefined();
     }
 
@@ -2985,9 +2985,9 @@ extern JS_PUBLIC_API(bool)
 JS_AllocateArrayBufferContents(JSContext *cx, uint32_t nbytes, void **contents, uint8_t **data);
 
 /*
- * Reallocate memory allocated by JS_AllocateArrayBufferContents, growing or shrinking it
- * as appropriate.  The new data pointer will be returned in data.  If *contents is NULL,
- * behaves like JS_AllocateArrayBufferContents.
+ * Reallocate memory allocated by JS_AllocateArrayBufferContents, growing or
+ * shrinking it as appropriate.  The new data pointer will be returned in data.
+ * If *contents is nullptr, behaves like JS_AllocateArrayBufferContents.
  */
 extern JS_PUBLIC_API(bool)
 JS_ReallocateArrayBufferContents(JSContext *cx, uint32_t nbytes, void **contents, uint8_t **data);
@@ -3084,7 +3084,7 @@ JS_GetSecurityCallbacks(JSRuntime *rt);
  * there is no available JSContext. Instead, the caller must ensure that the
  * given principals stays valid for as long as 'rt' may point to it. If the
  * principals would be destroyed before 'rt', JS_SetTrustedPrincipals must be
- * called again, passing NULL for 'prin'.
+ * called again, passing nullptr for 'prin'.
  */
 extern JS_PUBLIC_API(void)
 JS_SetTrustedPrincipals(JSRuntime *rt, const JSPrincipals *prin);
@@ -3137,8 +3137,8 @@ JS_GetFunctionId(JSFunction *fun);
  * Return a function's display name. This is the defined name if one was given
  * where the function was defined, or it could be an inferred name by the JS
  * engine in the case that the function was defined to be anonymous. This can
- * still return NULL if a useful display name could not be inferred. The same
- * restrictions on rooting as those in JS_GetFunctionId apply.
+ * still return nullptr if a useful display name could not be inferred. The
+ * same restrictions on rooting as those in JS_GetFunctionId apply.
  */
 extern JS_PUBLIC_API(JSString *)
 JS_GetFunctionDisplayId(JSFunction *fun);
@@ -3171,7 +3171,7 @@ JS_IsConstructor(JSFunction *fun);
 /*
  * Bind the given callable to use the given object as "this".
  *
- * If |callable| is not callable, will throw and return NULL.
+ * If |callable| is not callable, will throw and return nullptr.
  */
 extern JS_PUBLIC_API(JSObject*)
 JS_BindCallable(JSContext *cx, JSObject *callable, JSObject *newThis);
@@ -3332,8 +3332,8 @@ CanCompileOffThread(JSContext *cx, const CompileOptions &options);
  * for the compilation. The callback will be invoked while off the main thread,
  * so must ensure that its operations are thread safe. Afterwards,
  * FinishOffThreadScript must be invoked on the main thread to get the result
- * script or NULL. If maybecx is specified, this method will also report any
- * error or warnings generated during the parse.
+ * script or nullptr. If maybecx is specified, this method will also report
+ * any error or warnings generated during the parse.
  *
  * The characters passed in to CompileOffThread must remain live until the
  * callback is invoked, and the resulting script will be rooted until the call
@@ -3763,10 +3763,10 @@ JS_ConcatStrings(JSContext *cx, JS::HandleString left, JS::HandleString right);
  * For JS_DecodeBytes, set *dstlenp to the size of the destination buffer before
  * the call; on return, *dstlenp contains the number of jschars actually stored.
  * To determine the necessary destination buffer size, make a sizing call that
- * passes NULL for dst.
+ * passes nullptr for dst.
  *
  * On errors, the functions report the error. In that case, *dstlenp contains
- * the number of characters or bytes transferred so far.  If cx is NULL, no
+ * the number of characters or bytes transferred so far.  If cx is nullptr, no
  * error is reported on failure, and the functions simply return false.
  *
  * NB: This function does not store an additional zero byte or jschar after the
@@ -3820,7 +3820,7 @@ class JSAutoByteString
     }
 
     JSAutoByteString(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM)
-      : mBytes(NULL)
+      : mBytes(nullptr)
     {
         MOZ_GUARD_OBJECT_NOTIFIER_INIT;
     }
@@ -3853,7 +3853,7 @@ class JSAutoByteString
 
     void clear() {
         js_free(mBytes);
-        mBytes = NULL;
+        mBytes = nullptr;
     }
 
     char *ptr() const {
@@ -3933,14 +3933,14 @@ struct JSLocaleCallbacks {
 
 /*
  * Establish locale callbacks. The pointer must persist as long as the
- * JSRuntime.  Passing NULL restores the default behaviour.
+ * JSRuntime.  Passing nullptr restores the default behaviour.
  */
 extern JS_PUBLIC_API(void)
 JS_SetLocaleCallbacks(JSRuntime *rt, JSLocaleCallbacks *callbacks);
 
 /*
  * Return the address of the current locale callbacks struct, which may
- * be NULL.
+ * be nullptr.
  */
 extern JS_PUBLIC_API(JSLocaleCallbacks *)
 JS_GetLocaleCallbacks(JSRuntime *rt);
@@ -4182,9 +4182,9 @@ JS_DropExceptionState(JSContext *cx, JSExceptionState *state);
 /*
  * If the given value is an exception object that originated from an error,
  * the exception will contain an error report struct, and this API will return
- * the address of that struct.  Otherwise, it returns NULL.  The lifetime of
- * the error report struct that might be returned is the same as the lifetime
- * of the exception object.
+ * the address of that struct.  Otherwise, it returns nullptr.  The lifetime
+ * of the error report struct that might be returned is the same as the
+ * lifetime of the exception object.
  */
 extern JS_PUBLIC_API(JSErrorReport *)
 JS_ErrorFromException(JSContext *cx, JS::HandleValue v);
diff --git a/js/src/vm/ProxyObject.cpp b/js/src/vm/ProxyObject.cpp
index 6d520ec31306..9a658e598455 100644
--- a/js/src/vm/ProxyObject.cpp
+++ b/js/src/vm/ProxyObject.cpp
@@ -37,7 +37,7 @@ ProxyObject::New(JSContext *cx, BaseProxyHandler *handler, HandleValue priv, Tag
     if (proto.isObject() && !options.singleton()) {
         RootedObject protoObj(cx, proto.toObject());
         if (!JSObject::setNewTypeUnknown(cx, clasp, protoObj))
-            return NULL;
+            return nullptr;
     }
 
     NewObjectKind newKind =
@@ -47,7 +47,7 @@ ProxyObject::New(JSContext *cx, BaseProxyHandler *handler, HandleValue priv, Tag
         allocKind = GetBackgroundAllocKind(allocKind);
     RootedObject obj(cx, NewObjectWithGivenProto(cx, clasp, proto, parent, allocKind, newKind));
     if (!obj)
-        return NULL;
+        return nullptr;
 
     Rooted<ProxyObject*> proxy(cx, &obj->as<ProxyObject>());
     proxy->initHandler(handler);