Summary of common methods of Map

Map is a new data structure in ES6. It is added together with Set. In fact, the functions are similar. The following article mainly summarizes and introduces the common methods of Map in ES6 learning tutorials. The article introduces it in detail through sample code. Friends in need can refer to it. Let’s take a look together.

Preface

ES6 contains many new language features that will make JS more powerful and expressive. This article will give you a detailed introduction to the common methods of Map in ES6. Without further ado, let’s take a look at the detailed introduction:

1. Convert Map structure to array structure

A faster method is to use the spread operator (...)

let map = new Map([
 [1, 'one'],
 [2, 'two'],
 [3, 'three'],
]);
[...map.keys()]
// [1, 2, 3]
[...map.values()]
// ['one', 'two', 'three']
[...map.entries()]
// [[1,'one'], [2, 'two'], [3, 'three']]
[...map]
// [[1,'one'], [2, 'two'], [3, 'three']]

2 .Map loop traversal

Map natively provides three traversers:

• keys(): a traverser that returns key names.

• values(): Returns a traverser of key values.

• entries(): Returns a traverser of all members.

The following are usage examples.

let map = new Map([
 ['F', 'no'],
 ['T', 'yes'],
]);

for (let key of map.keys()) {
 console.log(key);
}
// "F"
// "T"

for (let value of map.values()) {
 console.log(value);
}
// "no"
// "yes"

for (let item of map.entries()) {
 console.log(item[0], item[1]);
}
// "F" "no"
// "T" "yes"

// 或者
for (let [key, value] of map.entries()) {
 console.log(key, value);
}

// 等同于使用map.entries()
for (let [key, value] of map) {
 console.log(key, value);
}

The last example of the above code represents the default iterator interface (Symbol.iterator attribute) of the Map structure, which is the entries method.

map[Symbol.iterator] === map.entries // true

3.Map Get the length

map.size;

4.Map Get the first element

##

const m = new Map();
m.set('key1', {})
m.set('keyN', {})

console.log(m.entries().next().value); // [ 'key1', {} ]

Get the first key

console.log(m.keys().next().value); // key1

Get the first value

console.log(m.values().next().value); // {}

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