The initial value of the @@iterator property is the same function object as the initial value of the entries method.
myMap[Symbol.iterator]
The map iterator function, which is the entries() function by default.
[@@iterator]()
const myMap = new Map();
myMap.set('0', 'foo');
myMap.set(1, 'bar');
myMap.set({}, 'baz');
const mapIter = myMap[Symbol.iterator]();
console.log(mapIter.next().value); // ["0", "foo"]
console.log(mapIter.next().value); // [1, "bar"]
console.log(mapIter.next().value); // [Object, "baz"]
[@@iterator]() with for..of
const myMap = new Map();
myMap.set('0', 'foo');
myMap.set(1, 'bar');
myMap.set({}, 'baz');
for (const entry of myMap) {
console.log(entry);
}
// ["0", "foo"]
// [1, "bar"]
// [{}, "baz"]
for (const [key, value] of myMap) {
console.log(`${key}: ${value}`);
}
// 0: foo
// 1: bar
// [Object]: baz
| Specification | Status | Comment |
|---|---|---|
| ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Map.prototype[@@iterator]()' in that specification. | Standard | Initial definition. |
| ECMAScript Latest Draft (ECMA-262) The definition of 'Map.prototype[@@iterator]()' in that specification. | Draft |
| Feature | Chrome | Edge | Firefox | Internet Explorer | Opera | Safari |
|---|---|---|---|---|---|---|
| Basic support | Yes | Yes |
17 — 271 364 |
No | Yes | Yes |
| Feature | Android webview | Chrome for Android | Edge mobile | Firefox for Android | Opera Android | iOS Safari | Samsung Internet |
|---|---|---|---|---|---|---|---|
| Basic support | Yes | Yes | Yes |
17 — 271 364 |
Yes | Yes | ? |
1. Supported as iterator.
2. A placeholder property named @@iterator is used.
3. Supported as @@iterator.
4. The @@iterator symbol is implemented.
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https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map/@@iterator