Bug 1440116 - Add an `ObjectUtils.isEmpty` helper. r=markh

MozReview-Commit-ID: 1Y4XW3dKUPT

--HG--
extra : rebase_source : 9a46656c876c8081e17f15427166f7b2ad9ad879

toolkit/modules/ObjectUtils.jsm

@@ -52,6 +52,26 @@ var ObjectUtils = {
    */
   strict(obj) {
     return _strict(obj);
+  },
+
+  /**
+   * Returns `true` if `obj` is an array without elements, an object without
+   * enumerable properties, or a falsy primitive; `false` otherwise.
+   */
+  isEmpty(obj) {
+    if (!obj) {
+      return true;
+    }
+    if (typeof obj != "object") {
+      return false;
+    }
+    if (Array.isArray(obj)) {
+      return !obj.length;
+    }
+    for (let key in obj) {
+      return false;
+    }
+    return true;
   }
 };
 

toolkit/modules/tests/xpcshell/test_ObjectUtils.js

@@ -107,3 +107,32 @@ add_task(async function test_deepEqual() {
 
   Assert.ok(deepEqual(checkEquiv(e, f), checkEquiv(f, e)));
 });
+
+add_task(async function test_isEmpty() {
+  Assert.ok(ObjectUtils.isEmpty(""), "Empty strings should be empty");
+  Assert.ok(ObjectUtils.isEmpty(0), "0 should be empty");
+  Assert.ok(ObjectUtils.isEmpty(NaN), "NaN should be empty");
+  Assert.ok(ObjectUtils.isEmpty(), "Undefined should be empty");
+  Assert.ok(ObjectUtils.isEmpty(null), "Null should be empty");
+  Assert.ok(ObjectUtils.isEmpty(false), "False should be empty");
+
+  Assert.ok(ObjectUtils.isEmpty({}),
+    "Objects without properties should be empty");
+  Assert.ok(ObjectUtils.isEmpty(Object.defineProperty({}, "a", {
+    value: 1,
+    enumerable: false,
+    configurable: true,
+    writable: true
+  })), "Objects without enumerable properties should be empty");
+  Assert.ok(ObjectUtils.isEmpty([]), "Arrays without elements should be empty");
+
+  Assert.ok(!ObjectUtils.isEmpty([1]),
+    "Arrays with elements should not be empty");
+  Assert.ok(!ObjectUtils.isEmpty({ a: 1 }),
+    "Objects with properties should not be empty");
+
+  function A() {}
+  A.prototype.b = 2;
+  Assert.ok(!ObjectUtils.isEmpty(new A()),
+    "Objects with inherited enumerable properties should not be empty");
+});