The [@@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.
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 @@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"]