Preface
Function binding is probably the point that everyone pays the least attention to when using JavaScript, but when you realize that you need a solution to how to solve it in another function When maintaining this context, what you really need is Function.prototype.bind(), but you may still not realize this.
The first time you encounter this problem, you may be tempted to set this to a variable so that you can continue to refer to it after changing the context.
1. The syntax of bind
The main function of the bind() method is to bind a function to an object. The bind() method will create a function, and the this object in the function body The value will be bound to the value passed into the bind() function.
1.1 Definition
bind() is defined as follows:
The bind() method creates a new function that, when called, has its this keyword set to the provided value , with a given sequence of arguments preceding any provided when the new function is called.
bind() function creates a new function (called a bound function), and the new function is the same as the called function (the bound function objective function) have the same function body. When the target function is called, the this value is bound to the first parameter of bind() and cannot be overridden.
1.2 Principle
You can use the following code to simulate the principle of bind():
Function.prototype.bind = function(context) { var self = this; // 保存原函数 return function() { // 返回一个新函数 return self.apply(context, arguments); // 执行新函数时,将传入的上下文context作为新函数的this } }
1.3 Syntax
Function.prototype.bind(thisArg[, arg1[, arg2[, ...]]])
2. Bind application scenarios
2.1 Implementing object inheritance
var A = function(name) { this.name = name; } var B = function() { A.bind(this, arguments); } B.prototype.getName = function() { return this.name; } var b = new B("hello"); console.log(b.getName()); // "hello"
2.2 Event processing
var paint = { color: "red", count: 0, updateCount: function() { this.count++; console.log(this.count); } }; // 事件处理函数绑定的错误方法: document.querySelector('button') .addEventListener('click', paint.updateCount); // paint.updateCount函数的this指向变成了该DOM对象 // 事件处理函数绑定的正确方法: document.querySelector('button') .addEventListener('click', paint.updateCount.bind(paint)); // paint.updateCount函数的this指向变成了paint
2.3 Time interval function
var notify = { text: "Hello World!", beforeRender: function() { alert(this.text); }, render: function() { // 错误方法: setTimeout(this.beforeRender, 0); // undefined // 正确方法: setTimeout(this.beforeRender.bind(this), 0); // "Hello World!" } }; notify.render();
2.4 Borrowing the native method of Array
var a = {}; Array.prototype.push.bind(a, "hello", "world")(); console.log(a); // "hello", "world"
3. Browser compatibility of bind() method
if (!Function.prototype.bind) { Function.prototype.bind = function() { var self = this, // 保存原函数 context = [].shift.call(arguments), // 需要绑定的this上下文 args = [].slice.call(arguments); // 剩余的参数转成数组 return function() { // 返回一个新函数 // 执行新函数时,将传入的上下文context作为新函数的this // 并且组合两次分别传入的参数,作为新函数的参数 return self.apply(context, [].concat.call(args, [].slice.call(arguments))); } }; }5. The difference between bind and call/apply methods Common points: can change the context of function execution; Differences: bind: does not execute the function immediately, generally used in asynchronous calls and events; call/apply: executes the function immediately. SummaryOkay, the above is the entire content of this article. I hope the content of this article can be helpful to everyone in learning or using Javascript. If you have any questions, you can leave a message to communicate. For more X-depth understanding of the Function.prototype.bind() method in JS and related articles, please pay attention to the PHP Chinese website!

Detailed explanation of JavaScript string replacement method and FAQ This article will explore two ways to replace string characters in JavaScript: internal JavaScript code and internal HTML for web pages. Replace string inside JavaScript code The most direct way is to use the replace() method: str = str.replace("find","replace"); This method replaces only the first match. To replace all matches, use a regular expression and add the global flag g: str = str.replace(/fi

This tutorial shows you how to integrate a custom Google Search API into your blog or website, offering a more refined search experience than standard WordPress theme search functions. It's surprisingly easy! You'll be able to restrict searches to y

So here you are, ready to learn all about this thing called AJAX. But, what exactly is it? The term AJAX refers to a loose grouping of technologies that are used to create dynamic, interactive web content. The term AJAX, originally coined by Jesse J

This article series was rewritten in mid 2017 with up-to-date information and fresh examples. In this JSON example, we will look at how we can store simple values in a file using JSON format. Using the key-value pair notation, we can store any kind

Leverage jQuery for Effortless Web Page Layouts: 8 Essential Plugins jQuery simplifies web page layout significantly. This article highlights eight powerful jQuery plugins that streamline the process, particularly useful for manual website creation

Core points This in JavaScript usually refers to an object that "owns" the method, but it depends on how the function is called. When there is no current object, this refers to the global object. In a web browser, it is represented by window. When calling a function, this maintains the global object; but when calling an object constructor or any of its methods, this refers to an instance of the object. You can change the context of this using methods such as call(), apply(), and bind(). These methods call the function using the given this value and parameters. JavaScript is an excellent programming language. A few years ago, this sentence was

jQuery is a great JavaScript framework. However, as with any library, sometimes it’s necessary to get under the hood to discover what’s going on. Perhaps it’s because you’re tracing a bug or are just curious about how jQuery achieves a particular UI

This post compiles helpful cheat sheets, reference guides, quick recipes, and code snippets for Android, Blackberry, and iPhone app development. No developer should be without them! Touch Gesture Reference Guide (PDF) A valuable resource for desig


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

AI Hentai Generator
Generate AI Hentai for free.

Hot Article

Hot Tools

mPDF
mPDF is a PHP library that can generate PDF files from UTF-8 encoded HTML. The original author, Ian Back, wrote mPDF to output PDF files "on the fly" from his website and handle different languages. It is slower than original scripts like HTML2FPDF and produces larger files when using Unicode fonts, but supports CSS styles etc. and has a lot of enhancements. Supports almost all languages, including RTL (Arabic and Hebrew) and CJK (Chinese, Japanese and Korean). Supports nested block-level elements (such as P, DIV),

SublimeText3 Linux new version
SublimeText3 Linux latest version

Notepad++7.3.1
Easy-to-use and free code editor

PhpStorm Mac version
The latest (2018.2.1) professional PHP integrated development tool

Dreamweaver CS6
Visual web development tools
