Home Web Front-end JS Tutorial Detailed explanation of Map and introduction to commonly used APIs

Detailed explanation of Map and introduction to commonly used APIs

Sep 26, 2017 am 09:39 AM
api introduce Commonly used

The following editor will bring you an es6 series tutorial_Detailed explanation of Map and introduction to commonly used APIs. The editor thinks it’s pretty good, so I’ll share it with you now and give it as a reference. Let’s follow the editor to take a look

The Map type in ECMAScript 6 is an ordered list that stores many key-value pairs. Key-value pairs support all data types. Keys 0 and '0' will be treated as two different keys, and no cast conversion will occur.

How to use Map?


let map = new Map();
Copy after login

Common methods:

set(key, value): Add a new key-value pair element

get(key): Get the value corresponding to the key. If the value does not exist, return undefined


let map = new Map();
map.set( '0', 'ghostwu' );
map.set( 0, 'ghostwu' );

console.log( map.get( '0' ) ); //ghostwu
console.log( map.get( 'name' ) ); //undefined;
Copy after login


let map = new Map();
var key1 = {}, key2 = {};

map.set( key1, 'ghostwu' );
map.set( key2, 22 );

console.log( map.get( key1 ) ); //ghostwu
console.log( map.get( key2 ) ); //22
Copy after login

Okay Use the object as the key of the Map. Although there are two empty objects, strong type conversion will not occur.

has( key): Determine whether the key name exists

delete( key): Delete key names and corresponding values

clear(): Remove all key-value pairs in the map collection

size: The number of elements in the map collection


let map = new Map();
map.set( 'name', 'ghostwu' );
map.set( 'age', 22 );

console.log( map.has( 'name' ) );//true
console.log( map.size ); //2

map.delete( 'name' );
console.log( map.has( 'name' ) );//false
console.log( map.size ); //1
console.log( map.has( 'age' ) ); //true

map.clear();
console.log( map.size ); //0
console.log( map.has( 'age' ) ); //false
Copy after login

Map supports array initialization, using a two-dimensional array, each array uses key-value pairs


let map = new Map( [ [ 'name', 'ghostwu' ], [ 'age', 22 ] ] );
console.log( map.has( 'name') ); //true
console.log( map.has( 'age') ); //true
console.log( map.size ); //2
map.set( 'sex', 'man' );
console.log( map.size );
console.log( map.get( 'name' ) ); //ghostwu
map.clear();
console.log( map.size ); //0
Copy after login

Map also supports the forEach method, support 2 parameters, the first one: function, the function supports 3 parameters (value, key, current map), the second one: this


let map = new Map( [ [ 'name', 'ghostwu' ], [ 'age', 22 ] ] );
map.set( 'sex', 'man' );
map.forEach( function( val, key, cur ){
 console.log( val, key, cur, this );
}, 100 );
Copy after login

The above is the detailed content of Detailed explanation of Map and introduction to commonly used APIs. For more information, please follow other related articles on the PHP Chinese website!

Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
2 weeks ago By 尊渡假赌尊渡假赌尊渡假赌
Repo: How To Revive Teammates
4 weeks ago By 尊渡假赌尊渡假赌尊渡假赌
Hello Kitty Island Adventure: How To Get Giant Seeds
4 weeks ago By 尊渡假赌尊渡假赌尊渡假赌

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

Detailed introduction to what wapi is Detailed introduction to what wapi is Jan 07, 2024 pm 09:14 PM

Users may have seen the term wapi when using the Internet, but for some people they definitely don’t know what wapi is. The following is a detailed introduction to help those who don’t know to understand. What is wapi: Answer: wapi is the infrastructure for wireless LAN authentication and confidentiality. This is like functions such as infrared and Bluetooth, which are generally covered near places such as office buildings. Basically they are owned by a small department, so the scope of this function is only a few kilometers. Related introduction to wapi: 1. Wapi is a transmission protocol in wireless LAN. 2. This technology can avoid the problems of narrow-band communication and enable better communication. 3. Only one code is needed to transmit the signal

Detailed explanation of whether win11 can run PUBG game Detailed explanation of whether win11 can run PUBG game Jan 06, 2024 pm 07:17 PM

Pubg, also known as PlayerUnknown's Battlegrounds, is a very classic shooting battle royale game that has attracted a lot of players since its popularity in 2016. After the recent launch of win11 system, many players want to play it on win11. Let's follow the editor to see if win11 can play pubg. Can win11 play pubg? Answer: Win11 can play pubg. 1. At the beginning of win11, because win11 needed to enable tpm, many players were banned from pubg. 2. However, based on player feedback, Blue Hole has solved this problem, and now you can play pubg normally in win11. 3. If you meet a pub

Introducing the latest Win 11 sound tuning method Introducing the latest Win 11 sound tuning method Jan 08, 2024 pm 06:41 PM

After updating to the latest win11, many users find that the sound of their system has changed slightly, but they don’t know how to adjust it. So today, this site brings you an introduction to the latest win11 sound adjustment method for your computer. It is not difficult to operate. And the choices are diverse, come and download and try them out. How to adjust the sound of the latest computer system Windows 11 1. First, right-click the sound icon in the lower right corner of the desktop and select "Playback Settings". 2. Then enter settings and click "Speaker" in the playback bar. 3. Then click "Properties" on the lower right. 4. Click the "Enhance" option bar in the properties. 5. At this time, if the √ in front of "Disable all sound effects" is checked, cancel it. 6. After that, you can select the sound effects below to set and click

Introduction to the skills and attributes of Hua Yishan Heart of the Moon Lu Shu Introduction to the skills and attributes of Hua Yishan Heart of the Moon Lu Shu Mar 23, 2024 pm 05:30 PM

In Hua Yishan Heart Moon, Lu Shu is an SSR celebrity. He is positioned as a single-target backline player and has a very impressive critical hit rate. Many players don’t know much about Lu Shu. Here’s what I’ve brought you. Come and take a look at the introduction to the skills and attributes of Hua Yishan Heart of the Moon Lu Shu. Celebrity Attributes Celebrity Skills 1. Lu Ming Shuzhong Skill Description: Lu Shu was born in Qiongqihui in Shuzhong. He has practiced martial arts since he was a child and has outstanding martial arts skills. Causes basic attack damage equal to 100% of the enemy's back row attack power, and reduces the target's rage by 10 points. Skill attributes: Level 2: Basic attack damage increased to 105%. Level 2: Basic attack damage is increased to 110%, and the target's rage is reduced by 15 points. Level 2: Basic attack damage increased to 115%. Level 2: Basic attack damage is increased to 120%, and the target's rage is reduced by 20 points. Level 2: Basic attack

PyCharm Beginner's Guide: Comprehensive Analysis of Replacement Functions PyCharm Beginner's Guide: Comprehensive Analysis of Replacement Functions Feb 25, 2024 am 11:15 AM

PyCharm is a powerful Python integrated development environment with rich functions and tools that can greatly improve development efficiency. Among them, the replacement function is one of the functions frequently used in the development process, which can help developers quickly modify the code and improve the code quality. This article will introduce PyCharm's replacement function in detail, combined with specific code examples, to help novices better master and use this function. Introduction to the replacement function PyCharm's replacement function can help developers quickly replace specified text in the code

Detailed information on the location of the printer driver on your computer Detailed information on the location of the printer driver on your computer Jan 08, 2024 pm 03:29 PM

Many users have printer drivers installed on their computers but don't know how to find them. Therefore, today I bring you a detailed introduction to the location of the printer driver in the computer. For those who don’t know yet, let’s take a look at where to find the printer driver. When rewriting content without changing the original meaning, you need to The language is rewritten to Chinese, and the original sentence does not need to appear. First, it is recommended to use third-party software to search. 2. Find "Toolbox" in the upper right corner. 3. Find and click "Device Manager" below. Rewritten sentence: 3. Find and click "Device Manager" at the bottom 4. Then open "Print Queue" and find your printer device. This time it is your printer name and model. 5. Right-click the printer device and you can update or uninstall it.

Detailed introduction of Samsung S24ai functions Detailed introduction of Samsung S24ai functions Jun 24, 2024 am 11:18 AM

2024 is the first year of AI mobile phones. More and more mobile phones integrate multiple AI functions. Empowered by AI smart technology, our mobile phones can be used more efficiently and conveniently. Recently, the Galaxy S24 series released at the beginning of the year has once again improved its generative AI experience. Let’s take a look at the detailed function introduction below. 1. Generative AI deeply empowers Samsung Galaxy S24 series, which is empowered by Galaxy AI and brings many intelligent applications. These functions are deeply integrated with Samsung One UI6.1, allowing users to have a convenient intelligent experience at any time, significantly improving the performance of mobile phones. Efficiency and convenience of use. The instant search function pioneered by the Galaxy S24 series is one of the highlights. Users only need to press and hold

Oracle API Usage Guide: Exploring Data Interface Technology Oracle API Usage Guide: Exploring Data Interface Technology Mar 07, 2024 am 11:12 AM

Oracle is a world-renowned database management system provider, and its API (Application Programming Interface) is a powerful tool that helps developers easily interact and integrate with Oracle databases. In this article, we will delve into the Oracle API usage guide, show readers how to utilize data interface technology during the development process, and provide specific code examples. 1.Oracle

See all articles