前端小知识点扫盲笔记记录13

原创

前端歌谣 2023-05-29 09:49:04 ©著作权

文章标签 ecmascript javascript 笔记开发语言前端 文章分类 JavaScript 前端开发

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前言

我是歌谣放弃很容易但是坚持一定很酷微信公众号关注前端小歌谣带你进入前端巅峰交流群今天继续对前端知识的小结

数组去重的方式

<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8" /> <meta http-equiv="X-UA-Compatible" content="IE=edge" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /> <title>数组去重的第二种方式</title> </head> <body> <div id="geyao"></div> </body> <script> var geyao = [1, 2, 3, 4, 6, 7, 1, 2, 3, 8, 9] function ArrayCommon(arr) { //判断是不是数组不是数组就返回一个false if (!Array.isArray(arr)) { console.log('这不是一个数组哦') return } //元素在数组中第一次出现的位置是否和元素现在的位置相等 return Array.prototype.filter.call(arr,function(item,index){ console.log(arr.indexOf(item),item,index) return arr.indexOf(item)===index }) } console.log(ArrayCommon(geyao, 'geyao')) // document.getElementById("geyao").innerText=ArrayCommon(geyao) </script> </html>

数组扁平化

<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8" /> <meta http-equiv="X-UA-Compatible" content="IE=edge" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /> <title>数组扁平化第一种方式循环</title> </head> <body> <script> let arr = [0, [1, [2, 3, [4, [5, 6]], 7]], [8, 9]] function geyao(arr) { var show = [] for (var i = 0; i < arr.length; i++) { //如果arr[i]是一个数组 if (Array.isArray(arr[i])) { //递归遍历arr[i] show.push.apply(show, geyao(arr[i])) } else { show.push(arr[i]) } } return show } console.log(geyao(arr)) //[0,1,2,3,4,5,6,7,8,9] </script> </body> </html>

数组扁平化reduce方法

```

reduce方法

数组方法splice

<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <title>数组方法splice</title> </head> <body> <script> //splice(start,end,index1,index2) 从什么位置开始，删几个？删了后插入什么新元素？ var geyao=["1","2","3","4"] var geyaotest=["1","2","3","4"] var geyaofangfang=["1","2","3","4"] var fangfang=["1","2","3","4"] var fangfangTest=["1","2","3","4"] var fangfangBang=["1","2","3","4"] var kangkang=["1","2","3","4"] var kangkangni=["1","2","3","4"] var kangkanghao=["1","2","3","4"] //1个参数会截取当前大于2之后的数都会被删除 geyao.splice(2) console.log(geyao,"geyao")//["1","2"] //2个参数表示从什么位置截取到什么位置把下标为2的截取掉 geyaotest.splice(2,1) console.log(geyaotest,"geyaotest") //[ "1", "2", "4" ] //3个参数在什么位置到什么位置添加 geyaofangfang.splice(2,1,"5") console.log(geyaofangfang,"geyaofangfang") //[ "1", "2", "5", "4" ] //超出数组长度默认获得前面的全部 fangfang.splice(5) console.log(fangfang,"fangfang") // [ "1", "2", "3", "4" ] //从5之后开始截取 fangfangTest.splice(5,1) console.log(fangfangTest,"fangfangTest") // [ "1", "2", "3", "4" ] //对后置的位置进行添加 fangfangBang.splice(5,1,"6") console.log(fangfangBang,"fangfangBang") // [ "1", "2", "3", "4","6"] //倒着开始截取剩余部分 kangkang.splice(-1) console.log(kangkang,"kangkang") // [ "1", "2", "3" ] //倒着进行处理 kangkangni.splice(-2,1) console.log(kangkangni,"kangkangni")//[ "1", "2", "4" ] //倒着插入对应值 kangkanghao.splice(-2,1,"8") console.log(kangkanghao,"kangkanghao")//[ "1", "2", "8", "4" ] //该方法向或者从数组中添加或者删除项目，返回被删除的项目。(该方法会改变原数组) </script> </body> </html>

数组特性

<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8" /> <meta http-equiv="X-UA-Compatible" content="IE=edge" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /> <title>数组特性</title> </head> <body> <script> // 数组空位 // 数组可以使用一串逗号来创建空位，逗号前面为一项，值为undefined // 改变length会直接作用于原数组： // 减小length会从数组尾部删除元素 // 增大length会向数组尾部添加值为undefined的元素 </script> </body> </html>