diff --git a/js/src/jsapi.cpp b/js/src/jsapi.cpp
index 4cac54dddf9b..fa380c290d7e 100644
--- a/js/src/jsapi.cpp
+++ b/js/src/jsapi.cpp
@@ -801,6 +801,7 @@ JSRuntime::JSRuntime()
     negativeInfinityValue(UndefinedValue()),
     positiveInfinityValue(UndefinedValue()),
     emptyString(NULL),
+    sourceHook(NULL),
     debugMode(false),
     spsProfiler(thisFromCtor()),
     profilingScripts(false),
diff --git a/js/src/jscntxt.h b/js/src/jscntxt.h
index 36ed62ac3fcc..a9a841abf4a1 100644
--- a/js/src/jscntxt.h
+++ b/js/src/jscntxt.h
@@ -716,6 +716,8 @@ struct JSRuntime : js::RuntimeFriendFields
         return !JS_CLIST_IS_EMPTY(&contextList);
     }
 
+    JS_SourceHook       sourceHook;
+
     /* Per runtime debug hooks -- see jsprvtd.h and jsdbgapi.h. */
     JSDebugHooks        debugHooks;
 
diff --git a/js/src/jsfriendapi.cpp b/js/src/jsfriendapi.cpp
index c0959b3bad76..465ac7dc4545 100644
--- a/js/src/jsfriendapi.cpp
+++ b/js/src/jsfriendapi.cpp
@@ -22,6 +22,12 @@
 using namespace js;
 using namespace JS;
 
+JS_FRIEND_API(void)
+JS_SetSourceHook(JSRuntime *rt, JS_SourceHook hook)
+{
+    rt->sourceHook = hook;
+}
+
 JS_FRIEND_API(void)
 JS_SetGrayGCRootsTracer(JSRuntime *rt, JSTraceDataOp traceOp, void *data)
 {
diff --git a/js/src/jsfriendapi.h b/js/src/jsfriendapi.h
index f71620f827a2..5b612d0c1bca 100644
--- a/js/src/jsfriendapi.h
+++ b/js/src/jsfriendapi.h
@@ -175,6 +175,11 @@ JS_END_EXTERN_C
 
 #ifdef __cplusplus
 
+typedef bool (* JS_SourceHook)(JSContext *cx, JSScript *script, char **src, uint32_t *length);
+
+extern JS_FRIEND_API(void)
+JS_SetSourceHook(JSRuntime *rt, JS_SourceHook hook);
+
 namespace js {
 
 struct RuntimeFriendFields {
diff --git a/js/src/jsfun.cpp b/js/src/jsfun.cpp
index e86d4aa45b1d..76f1e74e6b35 100644
--- a/js/src/jsfun.cpp
+++ b/js/src/jsfun.cpp
@@ -590,7 +590,10 @@ JSFunction::toString(JSContext *cx, bool bodyOnly, bool lambdaParen)
                 return NULL;
         }
     }
-    if (isInterpreted() && script()->source) {
+    bool haveSource = isInterpreted();
+    if (haveSource && !script()->source && !script()->loadSource(cx, &haveSource))
+            return NULL;
+    if (haveSource) {
         RootedString src(cx, script()->sourceData(cx));
         if (!src)
             return NULL;
@@ -686,6 +689,13 @@ JSFunction::toString(JSContext *cx, bool bodyOnly, bool lambdaParen)
             if (!out.append(")"))
                 return NULL;
         }
+    } else if (isInterpreted()) {
+        if ((!bodyOnly && !out.append("() {\n    ")) ||
+            !out.append("[sourceless code]") ||
+            (!bodyOnly && !out.append("\n}")))
+            return NULL;
+        if (!lambdaParen && (flags & JSFUN_LAMBDA) && (!out.append(")")))
+            return NULL;
     } else {
         JS_ASSERT(!(flags & JSFUN_EXPR_CLOSURE));
         if ((!bodyOnly && !out.append("() {\n    ")) ||
diff --git a/js/src/jsscript.cpp b/js/src/jsscript.cpp
index 3d44084724c6..f16278761850 100644
--- a/js/src/jsscript.cpp
+++ b/js/src/jsscript.cpp
@@ -1070,6 +1070,35 @@ SourceCompressorThread::waitOnCompression(SourceCompressionToken *userTok)
 }
 #endif /* JS_THREADSAFE */
 
+bool
+JSScript::loadSource(JSContext *cx, bool *worked)
+{
+    JS_ASSERT(!source);
+    *worked = false;
+    if (!cx->runtime->sourceHook)
+        return true;
+    char *src = NULL;
+    uint32_t length;
+    if (!cx->runtime->sourceHook(cx, this, &src, &length))
+        return false;
+    if (!src)
+        return true;
+    size_t newLength = length;
+    jschar *usrc = InflateString(cx, src, &newLength);
+    cx->free_(src);
+    if (!usrc)
+        return false;
+    ScriptSource *ss = ScriptSource::createFromSource(cx, usrc, length, false, NULL, true);
+    if (!ss) {
+        cx->free_(usrc);
+        return false;
+    }
+    source = ss;
+    ss->attachToRuntime(cx->runtime);
+    *worked = true;
+    return true;
+}
+
 JSFixedString *
 JSScript::sourceData(JSContext *cx)
 {
@@ -1147,7 +1176,8 @@ ScriptSource::substring(JSContext *cx, uint32_t start, uint32_t stop)
 
 ScriptSource *
 ScriptSource::createFromSource(JSContext *cx, const jschar *src, uint32_t length,
-                               bool argumentsNotIncluded, SourceCompressionToken *tok)
+                               bool argumentsNotIncluded, SourceCompressionToken *tok,
+                               bool ownSource)
 {
     ScriptSource *ss = static_cast<ScriptSource *>(cx->malloc_(sizeof(*ss)));
     if (!ss)
@@ -1160,6 +1190,7 @@ ScriptSource::createFromSource(JSContext *cx, const jschar *src, uint32_t length
     }
     ss->next = NULL;
     ss->length_ = length;
+    ss->compressedLength = 0;
     ss->marked = ss->onRuntime_ = false;
     ss->argumentsNotIncluded_ = argumentsNotIncluded;
 #ifdef DEBUG
@@ -1176,6 +1207,8 @@ ScriptSource::createFromSource(JSContext *cx, const jschar *src, uint32_t length
         ss->marked = true;
 #endif
 
+    JS_ASSERT_IF(ownSource, !tok);
+
 #ifdef JS_THREADSAFE
     if (tok) {
         tok->ss = ss;
@@ -1183,21 +1216,23 @@ ScriptSource::createFromSource(JSContext *cx, const jschar *src, uint32_t length
         cx->runtime->sourceCompressorThread.compress(tok);
     } else
 #endif
-        ss->considerCompressing(cx->runtime, src);
+        ss->considerCompressing(cx->runtime, src, ownSource);
 
 
     return ss;
 }
 
 void
-ScriptSource::considerCompressing(JSRuntime *rt, const jschar *src)
+ScriptSource::considerCompressing(JSRuntime *rt, const jschar *src, bool ownSource)
 {
     JS_ASSERT(!ready());
     const size_t memlen = length_ * sizeof(jschar);
     const size_t COMPRESS_THRESHOLD = 512;
 
     size_t compressedLen;
-    if (memlen >= COMPRESS_THRESHOLD &&
+    if (ownSource) {
+        data.source = const_cast<jschar *>(src);
+    } else if (memlen >= COMPRESS_THRESHOLD &&
         TryCompressString(reinterpret_cast<const unsigned char *>(src), memlen,
                           data.compressed, &compressedLen))
     {
@@ -1207,7 +1242,6 @@ ScriptSource::considerCompressing(JSRuntime *rt, const jschar *src)
         data.compressed = static_cast<unsigned char *>(mem);
         JS_ASSERT(data.compressed);
     } else {
-        compressedLength = 0;
         PodCopy(data.source, src, length_);
     }
 #ifdef DEBUG    
diff --git a/js/src/jsscript.h b/js/src/jsscript.h
index 6d8434d020ca..87ae8392d363 100644
--- a/js/src/jsscript.h
+++ b/js/src/jsscript.h
@@ -620,6 +620,8 @@ struct JSScript : public js::gc::Cell
 
     JSFixedString *sourceData(JSContext *cx);
 
+    bool loadSource(JSContext *cx, bool *worked);
+
     /* Return whether this script was compiled for 'eval' */
     bool isForEval() { return isCachedEval || isActiveEval; }
 
@@ -978,7 +980,8 @@ struct ScriptSource
                                           const jschar *src,
                                           uint32_t length,
                                           bool argumentsNotIncluded = false,
-                                          SourceCompressionToken *tok = NULL);
+                                          SourceCompressionToken *tok = NULL,
+                                          bool ownSource = false);
     void attachToRuntime(JSRuntime *rt);
     void mark() { JS_ASSERT(ready_); JS_ASSERT(onRuntime_); marked = true; }
     void destroy(JSRuntime *rt);
@@ -1000,7 +1003,7 @@ struct ScriptSource
 
   private:
     bool compressed() { return !!compressedLength; }
-    void considerCompressing(JSRuntime *rt, const jschar *src);
+    void considerCompressing(JSRuntime *rt, const jschar *src, bool ownSource = false);
 };
 
 #ifdef JS_THREADSAFE