头条面试题-创建一个Event类，并创建on、off、trigger、once方法

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我是靠谱客的博主纯真衬衫，这篇文章主要介绍头条面试题-创建一个Event类，并创建on、off、trigger、once方法，现在分享给大家，希望可以做个参考。

一、创建一个Event.js

复制代码

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class Event {
constructor() {
this.handlers = { // 记录所有的事件和处理函数

}
}
/* *
* on 添加事件监听
* @param type 事件类型
* @param handler 事件回调
* on('click', ()=>{})
* */
on(type, handler, once=false) {
if (!this.handlers[type]) {
this.handlers[type] = [];
}
if (!this.handlers[type].includes(handler)) {
this.handlers[type].push(handler);
handler.once = once;
}
}
/* *
* off 取消事件监听
*
*
*/
off(type, handler) {
if (this.handlers[type]) {
if (handler === undefined) {
this.handlers[type] = []
} else {
this.handlers[type] = this.handlers[type].filter((f)=>{
return f!=handler
})
}
}
}
/* *
* @param type 要执行哪个类型的函数
* @param eventData事件对象
* @param point this指向
*
*
*/
trigger(type, eventData = {}, point=this) {
if (this.handlers[type]) {
this.handlers[type].forEach(f => {
f.call(point, eventData);
if (f.once) {
this.off(type, f)
}
});
}
}
/* *
* once 函数执行一次
* @param type 事件处理
* @param handle 事件处理函数
*
*/
once(type, handler) {
this.on(type, handler, true);
}
}

二、使用Event.js

复制代码

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<style>
#box {
position: absolute;
top: 0;
left: 0;
width: 100px;
height: 100px;
background: red;
}
</style>
<script src="./event.js"></script>
</head>
<body>
<div id="box"></div>
<script>
/*
* 1.记录摁下时鼠标的位置和元素位置
* 鼠标位置-摁下时的鼠标位置 = 鼠标移动的位置
* 元素位置=鼠标移动距离+摁下时元素位置
**/
class Drag extends Event{
// 构造函数

constructor(el) {
super(); // 继承
this.el = el;
this.startOffset = null; // 鼠标摁下时元素的位置
this.startPoint = null; // 鼠标的坐标
let move = (e)=>{
this.move(e)
}
let end = (e)=>{
document.removeEventListener('mousemove', move);
document.removeEventListener('mouseup', end);
this.end(e)
}
el.addEventListener('mousedown', (e)=> {
this.start(e);
document.addEventListener('mousemove', move);
document.addEventListener('mouseup', end);
})
}
start(e) {
let {el} = this;
console.log(this)
console.log(el)
this.startOffset = {
x: el.offsetLeft,
y: el.offsetTop
}
this.startPoint = {
x: e.clientX,
y: e.clientY
}
this.trigger('dragstart', e, this.el)
}
end(e) {
this.trigger('dragend',e, this.el)
}
move(e) {
let {el, startOffset, startPoint} = this;
let nowPoint = {
x: e.clientX,
y: e.clientY
}
let dis = {
x: nowPoint.x - startPoint.x,
y: nowPoint.y - startPoint.y
}
el.style.left = dis.x + startOffset.x + 'px';
el.style.top = dis.y + startOffset.y + 'px';
this.trigger('dragmove', e, el)
}
}
(function() {
let box = document.querySelector('#box');
let dragBox = new Drag(box);
dragBox.on('dragstart', function(e) {
console.log(e);
console.log(this);
this.style.background = 'yellow';
})
dragBox.on('dragend', function(e) {
console.log('b')
this.style.background = 'blue';
})
dragBox.once('dragmove', function(e) {
console.log('c')
// this.style.background = 'blue';

})
console.log(dragBox)
})()
</script>
</body>
</html>

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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<style>
#box {
position: absolute;
top: 0;
left: 0;
width: 100px;
height: 100px;
background: red;
}
</style>
<script src="./event.js"></script>
</head>
<body>
<div id="box"></div>
<script>
/*
* 1.记录摁下时鼠标的位置和元素位置
* 鼠标位置-摁下时的鼠标位置 = 鼠标移动的位置
* 元素位置=鼠标移动距离+摁下时元素位置
**/
class Drag extends Event{
// 构造函数

constructor(el) {
super(); // 继承
this.el = el;
this.startOffset = null; // 鼠标摁下时元素的位置
this.startPoint = null; // 鼠标的坐标
let move = (e)=>{
this.move(e)
}
let end = (e)=>{
document.removeEventListener('mousemove', move);
document.removeEventListener('mouseup', end);
this.end(e)
}
el.addEventListener('mousedown', (e)=> {
this.start(e);
document.addEventListener('mousemove', move);
document.addEventListener('mouseup', end);
})
}
start(e) {
let {el} = this;
console.log(this)
console.log(el)
this.startOffset = {
x: el.offsetLeft,
y: el.offsetTop
}
this.startPoint = {
x: e.clientX,
y: e.clientY
}
this.trigger('dragstart', e, this.el)
}
end(e) {
this.trigger('dragend',e, this.el)
}
move(e) {
let {el, startOffset, startPoint} = this;
let nowPoint = {
x: e.clientX,
y: e.clientY
}
let dis = {
x: nowPoint.x - startPoint.x,
y: nowPoint.y - startPoint.y
}
el.style.left = dis.x + startOffset.x + 'px';
el.style.top = dis.y + startOffset.y + 'px';
this.trigger('dragmove', e, el)
}
}
(function() {
let box = document.querySelector('#box');
let dragBox = new Drag(box);
dragBox.on('dragstart', function(e) {
console.log(e);
console.log(this);
this.style.background = 'yellow';
})
dragBox.on('dragend', function(e) {
console.log('b')
this.style.background = 'blue';
})
dragBox.once('dragmove', function(e) {
console.log('c')
// this.style.background = 'blue';

})
console.log(dragBox)
})()
</script>
</body>
</html>