In-depth understanding of the Function.prototype.bind() method in JS
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paint2.3 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)));
}
};
}
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
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
What should I do if I encounter garbled code printing for front-end thermal paper receipts?
Apr 04, 2025 pm 02:42 PM
Frequently Asked Questions and Solutions for Front-end Thermal Paper Ticket Printing In Front-end Development, Ticket Printing is a common requirement. However, many developers are implementing...
Who gets paid more Python or JavaScript?
Apr 04, 2025 am 12:09 AM
There is no absolute salary for Python and JavaScript developers, depending on skills and industry needs. 1. Python may be paid more in data science and machine learning. 2. JavaScript has great demand in front-end and full-stack development, and its salary is also considerable. 3. Influencing factors include experience, geographical location, company size and specific skills.
Demystifying JavaScript: What It Does and Why It Matters
Apr 09, 2025 am 12:07 AM
JavaScript is the cornerstone of modern web development, and its main functions include event-driven programming, dynamic content generation and asynchronous programming. 1) Event-driven programming allows web pages to change dynamically according to user operations. 2) Dynamic content generation allows page content to be adjusted according to conditions. 3) Asynchronous programming ensures that the user interface is not blocked. JavaScript is widely used in web interaction, single-page application and server-side development, greatly improving the flexibility of user experience and cross-platform development.
How to merge array elements with the same ID into one object using JavaScript?
Apr 04, 2025 pm 05:09 PM
How to merge array elements with the same ID into one object in JavaScript? When processing data, we often encounter the need to have the same ID...
Is JavaScript hard to learn?
Apr 03, 2025 am 12:20 AM
Learning JavaScript is not difficult, but it is challenging. 1) Understand basic concepts such as variables, data types, functions, etc. 2) Master asynchronous programming and implement it through event loops. 3) Use DOM operations and Promise to handle asynchronous requests. 4) Avoid common mistakes and use debugging techniques. 5) Optimize performance and follow best practices.
How to achieve parallax scrolling and element animation effects, like Shiseido's official website?
or:
How can we achieve the animation effect accompanied by page scrolling like Shiseido's official website?
Apr 04, 2025 pm 05:36 PM
Discussion on the realization of parallax scrolling and element animation effects in this article will explore how to achieve similar to Shiseido official website (https://www.shiseido.co.jp/sb/wonderland/)...
The difference in console.log output result: Why are the two calls different?
Apr 04, 2025 pm 05:12 PM
In-depth discussion of the root causes of the difference in console.log output. This article will analyze the differences in the output results of console.log function in a piece of code and explain the reasons behind it. �...
The Evolution of JavaScript: Current Trends and Future Prospects
Apr 10, 2025 am 09:33 AM
The latest trends in JavaScript include the rise of TypeScript, the popularity of modern frameworks and libraries, and the application of WebAssembly. Future prospects cover more powerful type systems, the development of server-side JavaScript, the expansion of artificial intelligence and machine learning, and the potential of IoT and edge computing.
