A preliminary study on javascript custom events_javascript skills
Also, "Through the event mechanism, classes can be designed as independent modules and communicate externally through events, which improves program development efficiency.".I believe that C# programmers have a deep understanding of the benefits of events. Okay, Code is cheap. Look at the code:
function class1() { // The simplest event design pattern
}
class1.prototype = {
show: function () {
this .onShow();
},
onShow: function () { }
}
function test() {
var obj = new class1();
obj.onShow = function () {
alert( " test " );
}
obj.show();
}
Let’s see how to pass parameters to the event handler:
/ / Encapsulate the parameterized function into a parameterless function
function createFunction(obj, strFunc) {
var args = []; // Define args to store the parameters passed to the event handler
if ( ! obj) obj = window; // If it is a global function, obj=window;
// Get the parameters passed to the event handler
for ( var i = 2 ; i // Use a parameterless function to encapsulate the call of the event handler
return function () {
obj[strFunc].apply(obj, args); // Pass parameters to the specified event handler
}
}
function class1() {
}
class1.prototype = {
show: function () {
this .onShow();
},
onShow: function () { }
}
function objOnShow(userName) {
alert( " hello, " userName);
}
function test() {
var obj = new class1();
var userName = " test " ;
obj.onShow = createFunction( null , " objOnShow " , userName);
obj .show();
}
"Because the event mechanism only passes the name of a function without any parameter information, it cannot pass parameters in." This is something to be discussed later. "To solve This problem can be considered from the opposite way. Instead of considering how to pass parameters in, consider how to build an event handler without parameters. This program is created based on the event handler with parameters and is an outer layer. Encapsulation. ", the "program" here is the createFunction function, which cleverly uses the apply function to encapsulate functions with parameters into parameterless functions.Finally, let’s look at how to implement multi-binding of custom events:
// Make custom events support multi-binding
// Encapsulate functions with parameters into functions without parameters
function createFunction(obj , strFunc) {
var args = []; // Define args to store parameters passed to the event handler
if ( ! obj) obj = window; // If it is a global function, obj=window;
// Get the parameters passed to the event handler
for ( var i = 2 ; i // Use parameterless function Encapsulate the call of the event handler
return function () {
obj[strFunc].apply(obj, args); // Pass parameters to the specified event handler
}
}
function class1() {
}
class1.prototype = {
show: function () {
if ( this .onShow) {
for ( var i = 0 ; i this .onShow[i]();
}
}
},
attachOnShow: function (_eHandler) {
if ( ! this .onShow) { this .onShow = []; }
this .onShow.push(_eHandler);
}
}
function objOnShow(userName) {
alert( " hello, " userName);
}
function objOnShow2(testName) {
alert( " show: " testName);
}
function test() {
var obj = new class1() ;
var userName = " your name " ;
obj.attachOnShow(createFunction( null , " objOnShow " , userName));
obj.attachOnShow(createFunction( null , " objOnShow2 " , " test message " ));
obj.show();
}
We see that the basic idea of the attachOnShow method is to push the array. In fact, we can also remove the event processing after the event execution is completed. Function, implemented separately below:
// Encapsulate the function with parameters into a function without parameters
function createFunction(obj, strFunc) {
var args = []; // Define args for storage and transfer Parameters to the event handler
if ( ! obj) obj = window; // If it is a global function, obj=window;
// Get the parameters passed to the event handler
for ( var i = 2 ; i // Use a parameterless function to encapsulate the call of the event handler
return function () {
obj[strFunc] .apply(obj, args); // Pass parameters to the specified event handler
}
}
function class1() {
}
class1.prototype = {
show: function () {
if ( this .onShow) {
for ( var i = 0 ; i this .onShow[i]();
}
}
},
attachOnShow: function (_eHandler) { // Attach event
if ( ! this .onShow) { this .onShow = []; }
this . onShow.push(_eHandler);
},
detachOnShow: function (_eHandler) { // Remove event
if ( ! this .onShow) { this .onShow = []; }
this .onShow.pop(_eHandler);
}
}
function objOnShow(userName) {
alert( " hello, " userName);
}
function objOnShow2( testName) {
alert( " show: " testName);
}
function test() {
var obj = new class1();
var userName = " your name " ;
obj.attachOnShow(createFunction( null , " objOnShow " , userName));
obj.attachOnShow(createFunction( null , " objOnShow2 " , " test message " ));
obj.show();
obj.detachOnShow(createFunction( null , " objOnShow " , userName));
obj.show(); // Remove one and display the remaining one
obj.detachOnShow(createFunction( null , " objOnShow2 " , " test message " ));
obj.show(); // Remove both and display none
}
Let’s learn about custom events here first.

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.

JavaScript's application in the real world includes front-end and back-end development. 1) Display front-end applications by building a TODO list application, involving DOM operations and event processing. 2) Build RESTfulAPI through Node.js and Express to demonstrate back-end applications.


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