Map.prototype[@@iterator]()
The [@@iterator]()
method of Map
instances implements the iterable protocol and allows maps 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
Syntax
js
map[Symbol.iterator]()
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 @@iterator
method makes Map
objects iterable, and iterating syntaxes like the for...of
loop automatically calls this method to obtain the iterator to loop over.
js
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.
js
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 |
---|
ECMAScript Language Specification # sec-map.prototype-@@iterator |
Browser compatibility
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