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!

The future trends of Python and JavaScript include: 1. Python will consolidate its position in the fields of scientific computing and AI, 2. JavaScript will promote the development of web technology, 3. Cross-platform development will become a hot topic, and 4. Performance optimization will be the focus. Both will continue to expand application scenarios in their respective fields and make more breakthroughs in performance.

Both Python and JavaScript's choices in development environments are important. 1) Python's development environment includes PyCharm, JupyterNotebook and Anaconda, which are suitable for data science and rapid prototyping. 2) The development environment of JavaScript includes Node.js, VSCode and Webpack, which are suitable for front-end and back-end development. Choosing the right tools according to project needs can improve development efficiency and project success rate.

Yes, the engine core of JavaScript is written in C. 1) The C language provides efficient performance and underlying control, which is suitable for the development of JavaScript engine. 2) Taking the V8 engine as an example, its core is written in C, combining the efficiency and object-oriented characteristics of C. 3) The working principle of the JavaScript engine includes parsing, compiling and execution, and the C language plays a key role in these processes.

JavaScript is at the heart of modern websites because it enhances the interactivity and dynamicity of web pages. 1) It allows to change content without refreshing the page, 2) manipulate web pages through DOMAPI, 3) support complex interactive effects such as animation and drag-and-drop, 4) optimize performance and best practices to improve user experience.

C and JavaScript achieve interoperability through WebAssembly. 1) C code is compiled into WebAssembly module and introduced into JavaScript environment to enhance computing power. 2) In game development, C handles physics engines and graphics rendering, and JavaScript is responsible for game logic and user interface.

JavaScript is widely used in websites, mobile applications, desktop applications and server-side programming. 1) In website development, JavaScript operates DOM together with HTML and CSS to achieve dynamic effects and supports frameworks such as jQuery and React. 2) Through ReactNative and Ionic, JavaScript is used to develop cross-platform mobile applications. 3) The Electron framework enables JavaScript to build desktop applications. 4) Node.js allows JavaScript to run on the server side and supports high concurrent requests.

Python is more suitable for data science and automation, while JavaScript is more suitable for front-end and full-stack development. 1. Python performs well in data science and machine learning, using libraries such as NumPy and Pandas for data processing and modeling. 2. Python is concise and efficient in automation and scripting. 3. JavaScript is indispensable in front-end development and is used to build dynamic web pages and single-page applications. 4. JavaScript plays a role in back-end development through Node.js and supports full-stack development.

C and C play a vital role in the JavaScript engine, mainly used to implement interpreters and JIT compilers. 1) C is used to parse JavaScript source code and generate an abstract syntax tree. 2) C is responsible for generating and executing bytecode. 3) C implements the JIT compiler, optimizes and compiles hot-spot code at runtime, and significantly improves the execution efficiency of JavaScript.


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