Map.prototype[Symbol.iterator]()
Baseline
Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since September 2016.
The [Symbol.iterator]() method of Map instances implements the iterable protocol and allows Map objects to be consumed by most syntaxes expecting iterables, such as the spread syntax and for...of loops. It returns a map iterator object that yields the key-value pairs of the map in insertion order.
The initial value of this property is the same function object as the initial value of the Map.prototype.entries property.
Try it
const map = new Map();
map.set("0", "foo");
map.set(1, "bar");
const iterator = map[Symbol.iterator]();
for (const item of iterator) {
console.log(item);
}
// Expected output: Array ["0", "foo"]
// Expected output: Array [1, "bar"]
Syntax
map[Symbol.iterator]()
Parameters
None.
Return value
The same return value as Map.prototype.entries(): a new iterable iterator object that yields the key-value pairs of the map.
Examples
Iteration using for...of loop
Note that you seldom need to call this method directly. The existence of the [Symbol.iterator]() method makes Map objects iterable, and iterating syntaxes like the for...of loop automatically call this method to obtain the iterator to loop over.
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
Manually hand-rolling the iterator
You may still manually call the next() method of the returned iterator object to achieve maximum control over the iteration process.
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"]
Specifications
| Specification |
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| ECMAScript® 2027 Language Specification # sec-map.prototype-%symbol.iterator% |
Browser compatibility
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Legend
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- Full support
- Full support
- Uses a non-standard name
- Has more compatibility info.