How to define map in js

I have always used arrays and objects to define data models. When I was looking through ES6 syntax a few days ago, I suddenly discovered that there is a Map object that is particularly useful for operating key-value pairs, and the code is more concise and clear, which is great.

Today, we will learn step by step what a Map object is, and introduce to you the properties and methods of the Map object in detail. I hope that everyone will find another way to solve problems in data manipulation in the future. This is a new data structure in ECMA 6.

Definition

The Map object saves key/value pairs and is a collection of key/value pairs. Any value (object or primitive) can be used as a key or a value. The Object structure provides "string-value" correspondence, and the Map structure provides "value-value" correspondence.

Syntax:

mapObj=new Map([iterable]);

iterable can be an array or other iterable object, whose elements are either key-value pairs or an array of two elements. Each key-value pair is added to a new Map. null will be treated as undefined.

Map instance

All Map instances will inherit from Map.prototype.

Example

Map objects are similar to objects and are also collections of key-value pairs, but the scope of "keys" is not limited to strings, and various types of values ​​(including objects) can be used as keys.

let a=new Map();
let b={p:'Hello World'};
a.set(b,"content");
a.get(b);				//"content"
a.has(b)				//true
a.delete(b)				//true
a.has(b)   				//false

As a constructor, Map can also accept an array as a parameter. The members of this array are arrays representing key-value pairs.

let map=new Map(['first','aaaaaa'],['second','bbbbbb']);;
map.size();				//2
map.has('first');		//true
a.get(b);				//'aaaaaa'
map.has('second');		//true
a.get(b);				//'bbbbbb'

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