13个不low的JS数组操作

[1,[2,3]].flat(1) //[1,2,3][1,[2,3,[4,5]].flat(1) //[1,2,3,4,5][1,[2,3,[4,5]]].toString()  //‘1,2,3,4,5‘[1[2,3,[4,5[...]].flat(Infinity) //[1,2,3,4...n]

function flatten(arr) {    while(arr.some(item=>Array.isArray(item))) {        arr = [].concat(...arr);    }    return arr;}flatten([1,[2,3]]) //[1,2,3]flatten([1,[2,3,[4,5]]) //[1,2,3,4,5]

Array.from(new Set([1,2,3,3,4,4])) //[1,2,3,4][...new Set([1,2,3,3,4,4])] //[1,2,3,4]

Array.prototype.distinct = function(){ var arr = this,  result = [],  i,  j,  len = arr.length; for(i = 0; i < len; i++){  for(j = i + 1; j < len; j++){   if(arr[i] === arr[j]){    j = ++i;   }  }  result.push(arr[i]); } return result;}[1,2,3,3,4,4].distinct(); //[1,2,3,4]

[1,2,3,4].sort((a, b) => a - b); // [1, 2,3,4],默认是升序[1,2,3,4].sort((a, b) => b - a); // [4,3,2,1] 降序

Array.prototype.bubleSort=function () {    let arr=this,        len = arr.length;    for (let outer = len; outer >= 2; outer--) {      for (let inner = 0; inner <= outer - 1; inner++) {        if (arr[inner] > arr[inner + 1]) {          //升序          [arr[inner], arr[inner + 1]] = [arr[inner + 1], arr[inner]];          console.log([arr[inner], arr[inner + 1]]);        }      }    }    return arr;  }[1,2,3,4].bubleSort() //[1,2,3,4]

Array.prototype.selectSort=function () {        let arr=this,            len = arr.length;        for (let i = 0, len = arr.length; i < len; i++) {    for (let j = i, len = arr.length; j < len; j++) {      if (arr[i] > arr[j]) {        [arr[i], arr[j]] = [arr[j], arr[i]];      }    }  }    return arr;  }  [1,2,3,4].selectSort() //[1,2,3,4]

Math.max(...[1,2,3,4]) //4Math.max.apply(this,[1,2,3,4]) //4[1,2,3,4].reduce( (prev, cur,curIndex,arr)=> { return Math.max(prev,cur);},0) //4
Math.max()是Math对象内置的方法,参数是字符串;
reduce是ES5的数组api,参数有函数和默认初始值;
函数有四个参数,pre(上一次的返回值),cur(当前值),curIndex(当前值索引),arr(当前数组)

eval([1,2,3,4].join(‘+‘)] //10[1,2,3,4].arr.reduce((prev, cur) =>prev + cur) //10

function sum(arr) {  var len = arr.length;  if(len == 0){    return 0;  } else if (len == 1){    return arr[0];  } else {    return arr[0] + sum(arr.slice(1));  }}sum([1,2,3,4]) //10

[1,2,3,4].concat([5,6]) //[1,2,3,4,5,6][...[1,2,3,4],...[4,5]] //[1,2,3,4,5,6][1,2,3,4].push.apply([1,2,3,4],[5,6]) //[1,2,3,4,5,6]

let arr=[1,2,3,4];[5,6].map(item=>{   arr.push(item)}) //arr值为[1,2,3,4,5,6],注意不能直接return出来,return后只会返回[5,6]

[1,2,3].includes(4) //false[1,2,3].indexOf(4) //-1 如果存在换回索引[1, 2, 3].find((item)=>item===3)) //3 如果数组中无值返回undefined[1, 2, 3].findIndex((item)=>item===3)) //2 如果数组中无值返回-1
includes(),find(),findIndex()是ES6的api2.开始篇

[1,2,3].some(item=>{  return item===3}) //true 如果不包含返回false

Array.prototype.slice.call(arguments) //arguments是类数组(伪数组)Array.prototype.slice.apply(arguments)Array.from(arguments)[...arguments]

Array.prototype.slice = function(start,end){      var result = new Array();      start = start || 0;      end = end || this.length; //this指向调用的对象，当用了call后，能够改变this的指向，也就是指向传进来的对象，这是关键      for(var i = start; i < end; i++){           result.push(this[i]);      }      return result; } 

[1,2,3].fill(false) //[false,false,false]注:fill填充对象会报错
fill是ES6的方法 2.开始篇

[1,2,3].map(() => 0)

[1,2,3].every(item=>{return item>2}) //false

[1,2,3].some(item=>{return item>2}) //true

[1,2,3].filter(item=>{return item>2}) //[3]

Object.keys({name:‘张三‘,age:14}) //[‘name‘,‘age‘]Object.values({name:‘张三‘,age:14}) //[‘张三‘,14]Object.entries({name:‘张三‘,age:14}) //[[name,‘张三‘],[age,14]]Object.fromEntries([name,‘张三‘],[age,14]) //ES10的api,Chrome不支持 , firebox输出{name:‘张三‘,age:14}