Js tutorial Map

Map

The Map object holds key-value pairs and remembers the original insertion order of the keys. Any value (both objects and primitive values) may be used as either a key or a value.

const map1 = new Map();

map1.set("a", 1);
map1.set("b", 2);
map1.set("c", 3);

console.log(map1.get("a"));
// expected output: 1

map1.set("a", 97);

console.log(map1.get("a"));
// expected output: 97

console.log(map1.size);
// expected output: 3

map1.delete("b");

console.log(map1.size);
// expected output: 2

Map.prototype.entries()

The entries() method returns a new Iterator object that contains the [key, value] pairs for each element in the Map object in insertion order. In this particular case, this iterator object is also an iterable, so the for-of loop can be used. When the protocol [Symbol.iterator] is used, it returns a function that, when invoked, returns this iterator itself.

const map1 = new Map();

map1.set("0", "foo");
map1.set(1, "bar");

const iterator1 = map1.entries();

console.log(iterator1.next().value);
// expected output: ["0", "foo"]

console.log(iterator1.next().value);
// expected output: [1, "bar"]

Map.prototype.values()

The values() method returns a new Iterator object that contains the values for each element in the Map object in insertion order.

const map1 = new Map();

map1.set("0", "foo");
map1.set(1, "bar");

const iterator1 = map1.values();

console.log(iterator1.next().value);
// expected output: "foo"

console.log(iterator1.next().value);
// expected output: "bar"

Map.prototype.clear()

The clear() method removes all elements from a Map object.

const map1 = new Map();

map1.set("bar", "baz");
map1.set(1, "foo");

console.log(map1.size);
// expected output: 2

map1.clear();

console.log(map1.size);
// expected output: 0