41个最新的JavaScript开发技巧，你必须要知道

const arr1 = [1, 2, 3, 4, 5 , 8 ,9],arr2 = [5, 6, 7, 8, 9];
const intersection = arr1.filter(function (val) { return arr2.indexOf(val) > -1 })console.log(intersection) //[5, 8, 9]

const arr1 = [{ name: 'name1', id: 1 }, { name: 'name2', id: 2 }, { name: 'name3', id: 3 }, { name: 'name5', id: 5 }];const arr2 = [{ name: 'name1', id: 1 }, { name: 'name2', id: 2 }, { name: 'name3', id: 3 }, { name: 'name4', id: 4 }, { name: 'name5', id: 5 }];const result = arr2.filter(function (v) {return arr1.some(n => JSON.stringify(n) === JSON.stringify(v))})console.log(result); // [{ name: 'name1', id: 1 },{ name: 'name2', id: 2 },{ name: 'name3', id: 3 },{ name: 'name5', id: 5 }]

const arr1 = [1, 2, 3, 4, 5, 8, 9]const arr2 = [5, 6, 7, 8, 9];const result = arr1.concat(arr2.filter(v => !arr1.includes(v)))console.log(result) //[1, 2, 3, 4,5, 8, 9]

const arr1 = [{ name: 'name1', id: 1 }, { name: 'name2', id: 2 }, { name: 'name3', id: 3 }];const arr2 = [{ name: 'name1', id: 1 }, { name: 'name4', id: 4 }, { name: 'name5', id: 5 }];let arr3 = arr1.concat(arr2);let result = [];let obj = [];result = arr3.reduce(function (prev, cur, index, arr) {  obj[cur.id] ? '' : obj[cur.id] = true && prev.push(cur);  return prev;}, []);console.log(result); //[{ name: 'name1', id: 1 },{ name: 'name2', id: 2 },{ name: 'name3', id: 3 },{ name: 'name4', id: 4 },{ name: 'name5', id: 5 }]

const arr1 = [1, 2, 3, 4, 5, 8, 9]const arr2 = [5, 6, 7, 8, 9];const diff = arr1.filter(item => !new Set(arr2).has(item))console.log(diff) //[ 1, 2, 3, 4 ]

// 对象数组let arr1 = [{ name: 'name1', id: 1 }, { name: 'name2', id: 2 }, { name: 'name3', id: 3 }];let arr2 = [{ name: 'name1', id: 1 }, { name: 'name4', id: 4 }, { name: 'name5', id: 5 }];let result = arr1.filter(function (v) {  return arr2.every(n => JSON.stringify(n) !== JSON.stringify(v))})console.log(result); // [ { name: 'name2', id: 2 }, { name: 'name3', id: 3 } ]

const arr1 = [1, 2, 3, 4, 5, 8, 9]const arr2 = [5, 6, 7, 8, 9];const difference = Array.from(new Set(arr1.concat(arr2).filter(v => !new Set(arr1).has(v) || !new Set(arr2).has(v)))) console.log(difference) //[ 1, 2, 3, 4, 6, 7 ]

let arr1 = [{ name: 'name1', id: 1 }, { name: 'name2', id: 2 }, { name: 'name3', id: 3 }];let arr2 = [{ name: 'name1', id: 1 }, { name: 'name4', id: 4 }, { name: 'name5', id: 5 }];let arr3 = arr1.concat(arr2);let result = arr3.filter(function (v) {  return arr1.every(n => JSON.stringify(n) !== JSON.stringify(v)) || arr2.every(n => JSON.stringify(n) !== JSON.stringify(v))})console.log(result); // [{ name: 'name2', id: 2 },{ name: 'name3', id: 3 },{ name: 'name4', id: 4 },{ name: 'name5', id: 5 }]

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

const arr = [{ name: 'name1', id: 1 }, { name: 'name2', id: 2 }, { name: 'name3', id: 3 }, { name: 'name1', id: 1 }, { name: 'name4', id: 4 }, { name: 'name5', id: 5 }];const obj = [];const result = arr.reduce(function (prev, cur, index, arr) {  obj[cur.id] ? '' : obj[cur.id] = true && prev.push(cur);  return prev;}, []);console.log(result) //[{ name: 'name1', id: 1 },{ name: 'name2', id: 2 },{ name: 'name3', id: 3 },{ name: 'name4', id: 4 },{ name: 'name5', id: 5 }]

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

const arr1 = [{ name: "Rom", age: 12 }, { name: "Bob", age: 22 }].sort((a, b) => { return a.age - b.age })//升序const arr2 = [{ name: "Rom", age: 12 }, { name: "Bob", age: 22 }].sort((a, b) => { return -a.age + b.age })//降序console.log(arr2) // [{ name: 'Bob', age:22 }, { name: 'Rom', age: 12 }]console.log(arr1) // [ { name: 'Rom', age: 12 }, { name: 'Bob', age: 22 } ]

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

const arr = [{ id: 1, name: 'jack' },{ id: 2, name: 'may' },{ id: 3, name: 'shawn' },{ id: 4, name: 'tony' }]const arr1 = Math.max.apply(Math, arr.map(item => { return item.id }))const arr2 = arr.sort((a, b) => { return b.id - a.id })[0].idconsole.log(arr1) // 4console.log(arr2) // 4

[1, 2, 3, 4].reduce(function (prev, cur) {  return prev + cur;}, 0) //10 

const sum = [{age:1},{age:2}].reduce(function (prev, cur) {  return prev + cur.age;}, 0) //3console.log(sum)

const arr1 =[1, 2, 3, 4].concat([5, 6]) //[1,2,3,4,5,6]const arr2 =[...[1, 2, 3, 4],...[4, 5]] //[1,2,3,4,5,6]const arrA = [1, 2], arrB = [3, 4]const arr3 =Array.prototype.push.apply(arrA, arrB)//arrA值为[1,2,3,4]

const arr4 = [{ age: 1 }].concat([{ age: 2 }])const arr5 = [...[{ age: 1 }],...[{ age: 2 }]]console.log(arr4) //[ { age: 1 }, { age: 2 } ]console.log(arr5) // [ { age: 1 }, { age: 2 } ]

console.log([1, 2, 3].includes(4)) //falseconsole.log([1, 2, 3].indexOf(4)) //-1 如果存在换回索引console.log([1, 2, 3].find((item) => item === 3)) //3 如果数组中无值返回undefinedconsole.log([1, 2, 3].findIndex((item) => item === 3)) //2 如果数组中无值返回-1

const flag = [{age:1},{age:2}].some(v=>JSON.stringify(v)===JSON.stringify({age:2}))console.log(flag)

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

const arr = [{ age: 3 }, { age: 4 }, { age: 5 }]arr.every(item => { return item.age > 2 }) // true

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

const arr = [{ age: 3 }, { age: 4 }, { age: 5 }]arr.some(item => { return item.age < 4 }) // true

function sortNumber(a, b) {return a - b}const b = [1,2,3,7,5,6]const a = ["1.5", "1.5", "1.40", "1.25", "1.1000", "1.1"];
console.log(a.sort(sortNumber)); // [ 1, 2, 3, 5, 6, 7 ]console.log(b.sort(sortNumber)); //[ '1.1000', '1.1', '1.25', '1.40','1.5', '1.5' ] 

//假定字符串的每节数都在5位以下//去除数组空值||空格if (!Array.prototype.trim) {  Array.prototype.trim = function () {    let arr = []; this.forEach(function (e) {      if (e.match(/\S+/)) arr.push(e);    })    return arr;  }}
//提取数字部分function toNum(a) {  let d = a.toString();  let c = d.split(/\D/).trim();  let num_place = ["", "0", "00", "000", "0000"], r = num_place.reverse();  for (let i = 0; i < c.length; i++) {    let len = c[i].length;    c[i] = r[len] + c[i];  }  let res = c.join('');  return res;}
//提取字符function toChar(a) {  let d = a.toString();  let c = d.split(/\.|\d/).join('');  return c;}
function sortVersions(a, b) {
  let _a1 = toNum(a), _b1 = toNum(b);  if (_a1 !== _b1) return _a1 - _b1;  else {    _a2 = toChar(a).charCodeAt(0).toString(16);    _b2 = toChar(b).charCodeAt(0).toString(16);    return _a2 - _b2;  }}
let arr1 = ["10", "5", "40", "25", "1000", "1"];let arr2 = ["1.10", "1.5", "1.40", "1.25", "1.1000", "1.1"];let arr3 = ["1.10c", "1.10b", "1.10C", "1.25", "1.1000", "1.10A"];console.log(arr1.sort(sortVersions)) //[ '1', '5', '10', '25', '40', '1000' ]console.log(arr2.sort(sortVersions)) //[ '1.1', '1.5', '1.10', '1.25', '1.40', '1.1000' ]console.log(arr3.sort(sortVersions)) // [ '1.10A', '1.10C', '1.10b', '1.10c', '1.25', '1.1000' ]

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}

const arrName = ['张三', '李四', '王五']const arrAge=['20','30','40']const arrDec = ['描述1', '描述2', '描述3']const obj = arrName.map((item,index)=>{return { name: item, age: arrAge[index],dec:arrDec[index]}})
console.log(obj) // [{ name: '张三', age: '20', dec: '描述1' },{ name: '李四', age: '30', dec: '描述2' },{ name: '王五', age: '40', dec: '描述3' }]

const arr=[1,2]; //后面一定要加分号，因为不加解释器会认为在读数组[arr[1], arr[0]] = [arr[0], arr[1]]; // [2,1]

const flag = true;const obj = {    a: 0,    [flag ? "c" : "d"]: 2};// obj => { a: 0, c: 2 }

const { name, age, ...obj } = { name: '张三', age: 13, dec: '描述1', info: '信息' }console.log(name)  // 张三console.log(age)  // 13console.log(obj)  // {dec: '描述1', info: '信息' }

const { info:{ dec} } = { name: '张三', age: 13, info:{dec: '描述1', info: '信息' }}console.log(dec) // 描述1

const { name:newName } = { name: '张三', age: 13 }console.log(newName)  // 张三

const { dec='这是默认dec值' } = { name: '张三', age: 13 }console.log(dec) //这是默认dec值

let obj = { name: '', age: '', sex: '' },  defaultName = ["这是姓名默认值1", "这是年龄默认值1", "这是性别默认值1"];Object.keys(obj).forEach(key => {Object.defineProperty(obj, key, { // 拦截整个object 对象，并通过get获取值，set设置值，vue 2.x的核心就是这个来监听get() {return defaultName;    },set(value) {      defaultName = value;    }  });});
console.log(obj.name); // [ '这是姓名默认值1', '这是年龄默认值1', '这是性别默认值1' ]console.log(obj.age); // [ '这是姓名默认值1', '这是年龄默认值1', '这是性别默认值1' ]console.log(obj.sex); // [ '这是姓名默认值1', '这是年龄默认值1', '这是性别默认值1' ]obj.name = "这是改变值1";console.log(obj.name); // 这是改变值1console.log(obj.age);  // 这是改变值1console.log(obj.sex); // 这是改变值1
let objOne = {}, defaultNameOne = "这是默认值2";Object.defineProperty(obj, 'name', {get() {return defaultNameOne;  },set(value) {    defaultNameOne = value;  }});console.log(objOne.name); // undefinedobjOne.name = "这是改变值2";console.log(objOne.name); // 这是改变值2

let obj = { name: '', age: '', sex: '' }let handler = {get(target, key, receiver) {    console.log("get", key); return Reflect.get(target, key, receiver);  },set(target, key, value, receiver) {    console.log("set", key, value); // set name 李四  // set age 24return Reflect.set(target, key, value, receiver);  }};let proxy = new Proxy(obj, handler);proxy.name = "李四";proxy.age = 24;

const objDeepClone = obj => {return clone(obj)}
const isType = (obj, type) => {if (typeof obj !== 'object') return false;// 判断数据类型的经典方法：const typeString = Object.prototype.toString.call(obj);  let flag;switch (type) {case 'Array':      flag = typeString === '[object Array]';break;case 'Date':      flag = typeString === '[object Date]';break;case 'RegExp':      flag = typeString === '[object RegExp]';break;default:      flag = false;  }return flag;};
/*** deep clone* @param  {[type]} parent object 需要进行克隆的对象* @return {[type]}        深克隆后的对象*/const clone = parent => {// 维护两个储存循环引用的数组const parents = []const children = []
const _clone = parent => {if (parent === null) return nullif (typeof parent !== 'object') return parent
    let child, proto
if (isType(parent, 'Array')) {// 对数组做特殊处理      child = []    } else if (isType(parent, 'RegExp')) {// 对正则对象做特殊处理      child = new RegExp(parent.source, getRegExp(parent))if (parent.lastIndex) child.lastIndex = parent.lastIndex    } else if (isType(parent, 'Date')) {// 对Date对象做特殊处理      child = new Date(parent.getTime())    } else {// 处理对象原型      proto = Object.getPrototypeOf(parent)// 利用Object.create切断原型链      child = Object.create(proto)    }
// 处理循环引用const index = parents.indexOf(parent)
if (index !== -1) {// 如果父数组存在本对象,说明之前已经被引用过,直接返回此对象return children[index]    }    parents.push(parent)    children.push(child)
for (const i in parent) {// 递归      child[i] = _clone(parent[i])    }
return child  }return _clone(parent)}
console.log(objDeepClone({   name: '张三', age: 23,   obj: { name: '李四', age: 46},  arr:[1,2,3]})) // { name: '张三', age: 23, obj: { name: '李四', age: 46 }, arr:[ 1, 2, 3 ] } 

function deepCompare(x, y) {var i, l, leftChain, rightChain;
function compare2Objects(x, y) {var p;
// remember that NaN === NaN returns false// and isNaN(undefined) returns trueif (isNaN(x) && isNaN(y) && typeof x === 'number' && typeof y === 'number') {return true;    }
// Compare primitives and functions.     // Check if both arguments link to the same object.// Especially useful on the step where we compare prototypesif (x === y) {return true;    }
// Works in case when functions are created in constructor.// Comparing dates is a common scenario. Another built-ins?// We can even handle functions passed across iframesif ((typeof x === 'function' && typeof y === 'function') ||      (x instanceof Date && y instanceof Date) ||      (x instanceof RegExp && y instanceof RegExp) ||      (x instanceof String && y instanceof String) ||      (x instanceof Number && y instanceof Number)) {return x.toString() === y.toString();    }
// At last checking prototypes as good as we canif (!(x instanceof Object && y instanceof Object)) {return false;    }
if (x.isPrototypeOf(y) || y.isPrototypeOf(x)) {return false;    }
if (x.constructor !== y.constructor) {return false;    }
if (x.prototype !== y.prototype) {return false;    }
// Check for infinitive linking loopsif (leftChain.indexOf(x) > -1 || rightChain.indexOf(y) > -1) {return false;    }
// Quick checking of one object being a subset of another.// todo: cache the structure of arguments[0] for performancefor (p in y) {if (y.hasOwnProperty(p) !== x.hasOwnProperty(p)) {return false;      } else if (typeof y[p] !== typeof x[p]) {return false;      }    }
for (p in x) {if (y.hasOwnProperty(p) !== x.hasOwnProperty(p)) {return false;      } else if (typeof y[p] !== typeof x[p]) {return false;      }
switch (typeof (x[p])) {case 'object':case 'function':
          leftChain.push(x);          rightChain.push(y);
if (!compare2Objects(x[p], y[p])) {return false;          }
          leftChain.pop();          rightChain.pop();break;
default:if (x[p] !== y[p]) {return false;          }break;      }    }
return true;  }
if (arguments.length < 1) {return true;   }
for (i = 1, l = arguments.length; i < l; i++) {
    leftChain = []; //Todo: this can be cached    rightChain = [];
if (!compare2Objects(arguments[0], arguments[i])) {return false;    }  }
return true;}
const obj1 = { name: '张三', age: 23, obj: { name: '李四', age: 46 }, arr: [1, 2, 3],date:new Date(23),reg: new RegExp('abc'),fun: ()=>{} }const obj2 = { name: '张三', age: 23, obj: { name: '李四', age: 46 }, arr: [1, 2, 3],date: new Date(23),reg: new RegExp('abc'),fun: ()=>{} }console.log(deepCompare(obj1,obj2)) // true

'the Math object:' + Math.ceil(3.4)                // "the Math object:4"'the JSON object:' + {name:'曹操'}              // "the JSON object:[object Object]"

2  * { valueOf: ()=>'4' }                // 8'J' + { toString: ()=>'ava' }                // "Java"

'' + {toString:()=>'S',valueOf:()=>'J'}  //J

(()=>3)()  //3(()=>(3))()

const Func = function() {}(); // 常用
(function() {})(); // 常用(function() {}()); // 常用[function() {}()];
new function() {};new function() {}();void function() {}();typeof function() {}();delete function() {}();
+ function() {}();- function() {}();~ function() {}();! function() {}();

Promise.reject('这是第二个 reject 值').then((data)=>{console.log(data)}).catch(data=>{console.log(data) //这是第二个 reject 值})

function* gen(x) {const y = yield x + 6;return y;}
// yield 如果用在另外一个表达式中,要放在()里面// 像上面如果是在=右边就不用加()function* genOne(x) {const y = `这是第一个 yield 执行:${yield x + 1}`;return y;}
const g = gen(1);//执行 Generator 会返回一个Object,而不是像普通函数返回return 后面的值g.next() // { value: 7, done: false }//调用指针的 next 方法,会从函数的头部或上一次停下来的地方开始执行，直到遇到下一个 yield 表达式或return语句暂停,也就是执行yield 这一行// 执行完成会返回一个 Object,// value 就是执行 yield 后面的值,done 表示函数是否执行完毕g.next() // { value: undefined, done: true }// 因为最后一行 return y 被执行完成,所以done 为 true

function getSomething() {return "something";}async function testAsync() {return Promise.resolve("hello async");}async function test() {const v1 = await getSomething();const v2 = await testAsync();console.log(v1, v2); //something 和 hello async}test();

function reverseStr(str = "") {return str.split("").reduceRight((t, v) => t + v);}
const str = "reduce123";console.log(reverseStr(str)); // "123recuder"

function stringifyUrl(search = {}) {return Object.entries(search).reduce((t, v) => `${t}${v[0]}=${encodeURIComponent(v[1])}&`,Object.keys(search).length ? "?" : ""  ).replace(/&$/, "");}
console.log(stringifyUrl({ age: 27, name: "YZW" })); // "?age=27&name=YZW"

function parseUrlSearch() {const search = '?age=25&name=TYJ'return search.replace(/(^\?)|(&$)/g, "").split("&").reduce((t, v) => {const [key, val] = v.split("=");    t[key] = decodeURIComponent(val);return t;  }, {});}
console.log(parseUrlSearch()); // { age: "25", name: "TYJ" }

const val = 1 + ""; // 通过+ ''空字符串转化console.log(val); // "1"console.log(typeof val); // "string"
const val1 = String(1);console.log(val1); // "1"console.log(typeof val1); // "string"

function thousandNum(num = 0) {const str = (+num).toString().split(".");const int = nums => nums.split("").reverse().reduceRight((t, v, i) => t + (i % 3 ? v : `${v},`), "").replace(/^,|,$/g, "");const dec = nums => nums.split("").reduce((t, v, i) => t + ((i + 1) % 3 ? v : `${v},`), "").replace(/^,|,$/g, "");return str.length > 1 ? `${int(str[0])}.${dec(str[1])}` : int(str[0]);}
thousandNum(1234); // "1,234"thousandNum(1234.00); // "1,234"thousandNum(0.1234); // "0.123,4"console.log(thousandNum(1234.5678)); // "1,234.567,8"

'32' * 1            // 32'ds' * 1            // NaNnull * 1            // 0undefined * 1    // NaN1  * { valueOf: ()=>'3' }        // 3

+ '123'            // 123+ 'ds'               // NaN+ ''                    // 0+ null              // 0+ undefined    // NaN+ { valueOf: ()=>'3' }    // 3

Number.EPSILON=(function(){   //解决兼容性问题return Number.EPSILON?Number.EPSILON:Math.pow(2,-52);})();//上面是一个自调用函数，当JS文件刚加载到内存中，就会去判断并返回一个结果function numbersequal(a,b){ return Math.abs(a-b)  }//接下来再判断   const a=0.1+0.2, b=0.3;console.log(numbersequal(a,b)); //这里就为true了

~~7.5                // 7Math.ceil(7.5)       // 8Math.floor(7.5)      // 7

~~-7.5            // -7Math.floor(-7.5)     // -8Math.ceil(-7.5)      // -7

3.3 | 0         // 3-3.9 | 0        // -3
parseInt(3.3)  // 3parseInt(-3.3) // -3
// 四舍五入取整Math.round(3.3) // 3Math.round(-3.3) // -3
// 向上取整Math.ceil(3.3) // 4Math.ceil(-3.3) // -3
// 向下取整Math.floor(3.3) // 3Math.floor(-3.3) // -4

const num=5;!!(num & 1) // true!!(num % 2) // true

function dataTypeJudge(val, type) {const dataType = Object.prototype.toString.call(val).replace(/\[object (\w+)\]/, "$1").toLowerCase();return type ? dataType === type : dataType;}console.log(dataTypeJudge("young")); // "string"console.log(dataTypeJudge(20190214)); // "number"console.log(dataTypeJudge(true)); // "boolean"console.log(dataTypeJudge([], "array")); // trueconsole.log(dataTypeJudge({}, "array")); // false

const compact = arr => arr.filter(Boolean)compact([0, 1, false, 2, '', 3, 'a', 'e' * 23, NaN, 's', 34])  //[ 1, 2, 3, 'a', 's', 34 ]

const flag = false || true //true// 某个值为假时可以给默认值const arr = false || []

const flag1 = false && true //falseconst flag2 = true && true //true

switch(a) {case '张三':return 'age是12'case '李四':return 'age是120'}
// 使用对象替换后const obj ={'张三': 'age12','李四': 'age120',}console.log(obj['张三'])