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后盾人JS--闭包明明白白

news 2025/7/28 3:11:18

延伸函数环境生命周期

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head>
<body><script>function hd(){let n = 1return function sum(){let m =1return function show(){console.log(++m)}}}let a = hd()()a()a()</script>
</body>
</html>

构造函数中的作用域的使用形态

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head>
<body><script>function Hd(){let n = 1this.sum = function(){console.log(++n)}}let a = new Hd()a.sum()a.sum()a.sum()</script>
</body>
</html>

模拟出var的伪块作用域

var没有块级作用域，但是有函数作用域

这样可以顺利打印出i：

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head>
<body><script>for(var i=1;i<=3;i++){(function(i){setTimeout(function(){console.log(i)},1000)})(i)}</script>
</body>
</html>

闭包获取价格区间

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head>
<body><script>let arr = [1,23,4,5,6,7,8,9]function between(a,b){return function(v){return v>=a && v<=b}}console.log(arr.filter(between(3,9)))</script>
</body>
</html>

闭包动画

<!DOCTYPE html>
<html lang="en"><head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head>
<style>button {position: absolute}
</style><body><button message="后盾人">houdunren</button><script>let btns = document.querySelectorAll("button")btns.forEach(function (item) {item.addEventListener("click", function () {let left = 1setInterval(function () {item.style.left = left++ + "px"}, 5)})})</script>
</body></html>

只要这样就可以防抖（直接是父级环境）：

<!DOCTYPE html>
<html lang="en"><head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head>
<style>button {position: absolute}
</style><body><button message="后盾人">houdunren</button><script>let btns = document.querySelectorAll("button")btns.forEach(function (item) {let left = 1item.addEventListener("click", function () {setInterval(function () {item.style.left = left++ + "px"}, 5)})})</script>
</body></html>

但是虽然不抖了，引来了加速的效果。。。

加一个判断条件，就只会执行一次了：

<!DOCTYPE html>
<html lang="en"><head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head>
<style>button {position: absolute}
</style><body><button message="后盾人">houdunren</button><script>let btns = document.querySelectorAll("button")btns.forEach(function (item) {let left = 1let interval = falseitem.addEventListener("click", function () {if(!interval){interval = truesetInterval(function () {item.style.left = left++ + "px"}, 5)}})})</script>
</body></html>

闭包排序

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head>
<body><script>let lessons = [{title:"媒体查询响应式布局",click:89,price:12},{title:"FLEX弹性盒模型",click:45,price:120},{title:"GRID栅格系统",click:19,price:67},{title:"盒子模型详解",click:29,price:52}]function order(field){return function(a,b){return a[field] > b[field] ? 1 : -1}}let hd = lessons.sort(order("price"))console.table(hd)</script>
</body>
</html>

垃圾回收机制

当闭包不再使用时，手动解除对闭包函数和相关变量的引用，让垃圾回收机制能够回收这些内存。

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head>
<body><div desc="houdunren">在线学习</div><div desc="hdcms">开源产品</div><script>let divs = document.querySelectorAll('div')divs.forEach(function(item){item.addEventListener("click",function(){console.log(item)})item = null})</script>
</body>
</html>

this遗留问题

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head>
<body><script>let hd = {user:"后盾人",get: function(){let This = thisreturn function(){return This.user}}}let a = hd.get()console.log(a())</script>
</body>
</html>

也可以使用箭头函数：

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head>
<body><script>let hd = {user:"后盾人",get: function(){let This = thisreturn ()=>{return this.user}}}let a = hd.get()console.log(a())</script>
</body>
</html>