javascript event function?

javascript event function

In front-end development, javascript is an important programming language. The most commonly used one is the event function. Event functions are a key component in handling user interaction, making user input and interaction the core of a website or application. In this article, we'll explore the basics, common types, and usage of JavaScript event functions, and how to use them to write more powerful applications.

What is a javascript event function?

javascript event function is a JavaScript function that is called when various events occur in a web page or application. Common events include mouse clicks, mouse movements, keyboard taps, scrolling, etc. When an event occurs, JavaScript will automatically call the corresponding event function. Developers can add custom logic through event functions to achieve richer user interaction functions.

The basic syntax of the javascript event function is as follows:

element.event = function() {
    //执行代码
};

Among them, element is the element on the page, and event is the event type that needs to be responded to, such as click, mousemove, mouseover, etc. When the event is triggered, the defined function will be executed.

Common javascript event types

There are many commonly used event types in javascript. Here are some common event types:

1. Click event (click)

The click event is one of the most common event types. This event is fired when the user clicks. The common syntax is as follows:

element.onclick = function() {
  //执行代码
};

2. Mousemove event (mousemove)

The mousemove event occurs when the mouse moves on an element. You can use it to implement various mouseover effects and interact based on mouse position. The common syntax is as follows:

element.onmousemove = function(event) {
    //执行代码，event 对象包含有关鼠标指针位置的信息。
};

3. Keyboard events (keyup and keydown)

Keyup and keydown events are two common ways to handle keyboard events. Keyup occurs when the user releases a key; keydown occurs when the user presses a key. The common syntax for these events is as follows:

element.onkeyup = function(event) {
    //执行代码
};

element.onkeydown = function(event) {
    //执行代码
};

4. Scroll event (scroll)

scroll event is triggered when the document or element is scrolled. It can be used to create custom scroll bars, smooth scrolling, lazy loading and other functions. The common syntax is as follows:

element.onscroll = function() {
    //执行代码
};

5. Right-click menu event (contextmenu)

contextmenu event occurs when the user right-clicks. You can use it to customize the right-click menu and context. Commonly used syntax is as follows:

element.oncontextmenu = function() {
    //执行代码
};

Advanced usage of javascript event function

In addition to the above basic usage, javascript event function also has other advanced usage, which allows you to better control the interaction of the user interface.

1. Event Broker

Event Broker is an efficient way to handle a large number of events. Using event delegation, you can delegate events to a parent element and then trigger events based on child elements. This can help you reduce the amount of code and improve performance.

document.addEventListener('click', function(event) {
    if (event.target.classList.contains('myClass')) {
        //执行代码
    }
});

In the above code, we delegate the "click" event to the document element, and then trigger the event based on whether the target element has the "myClass" class.

2. Cancel default behavior

When the user's interaction with the page triggers the default behavior, such as clicking a link, submitting a form, etc., you can use the preventDefault() function to prevent the default behavior. occurrence of behavior.

element.onclick = function(event) {
    event.preventDefault(); //阻止链接跳转
    //执行代码
};

In the above code, we use the preventDefault() function to prevent the default behavior when the link is clicked, and then execute the custom code.

Summary

Javascript event functions can provide you with rich and flexible user interaction functions. In this article, we learned the basics of JavaScript event functions, introduced common event types and usage, and introduced advanced usage such as using event proxies and canceling default behaviors. I hope this article can be helpful to readers who are learning javascript and provide support for you to develop better applications.

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