JS: Map Object Tutorial

What is Map Object

• Map object is a collections of key/value pairs. Each pair is called a entry.
• Key can be any Value Types.
• Value can be any value types.
• Keys are always distinct.
• The insertion order of entries are maintained.

The map object is designed to be used as a map data structure (similar to Python Dictionary or Ruby Hash Table or Java Map. ).

Create Map

new Map()

Create a empty map.

new Map(iterable)

Create a map from values in iterable object iterable.

〔see Iterable Object〕

const xx = new Map();

// add new item
xx.set(1, "n1");
xx.set(2, "n2");

console.log(xx);
// Map { 1 => "n1", 2 => "n2" }

Parent of Map Objects

The parent of any map object is Map.prototype.

• JS: Prototype and Inheritance
• JS: Map.prototype

Add, Modify Entry

• JS: Map.prototype.set

Delete Entry

• JS: Map.prototype.delete

Check Key Existence

• JS: Map.prototype.has

Get Key's Value

• JS: Map.prototype.get

Size of Map

• JS: Map.prototype.size

Clear Map

• JS: Map.prototype.clear

Iterate Map

• JS: Iterate Map Object

Get All Keys

• JS: Map.prototype.keys

Get All Values

• JS: Map.prototype.values

Add Arbitrary Properties to Map

Because map is a object, you can add object properties to it, but you shouldn't do it.

const xx = new Map([[3, "n3"], [4, "n4"], [5, "n5"]]);

// you can add arbitrary properties to a map object
xx.pp = 22;
console.log(xx.pp === 22);