提升效率的JavaScript简写技巧有哪些

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简写技巧

当同时声明多个变量时，可简写成一行

//Longhandlet x;let y = 20; //Shorthandlet x, y = 20;

利用解构，可为多个变量同时赋值

//Longhandlet a, b, c;a = 5;b = 8;c = 12;//Shorthandlet [a, b, c] = [5, 8, 12];

巧用三元运算符简化if else

//Longhand let marks = 26; let result; if (marks >= 30) {   result = 'Pass'; } else {    result = 'Fail'; } //Shorthand let result = marks >= 30 ? 'Pass' : 'Fail';

使用||运算符给变量指定默认值

本质是利用了||运算符的特点，当前面的表达式的结果转成布尔值为false时，则值为后面表达式的结果

//Longhandlet imagePath;let path = getImagePath();if (path !== null && path !== undefined && path !== '') {    imagePath = path;} else {    imagePath = 'default.jpg';}//Shorthandlet imagePath = getImagePath() || 'default.jpg';

使用&&运算符简化if语句

例如某个函数在某个条件为真时才调用，可简写

//Longhandif (isLoggedin) {    goToHomepage(); }//ShorthandisLoggedin && goToHomepage();

使用解构交换两个变量的值

let x = 'Hello', y = 55;//Longhandconst temp = x;x = y;y = temp;//Shorthand[x, y] = [y, x];

适用箭头函数简化函数

//Longhandfunction add(num1, num2) {  return num1 + num2;}//Shorthandconst add = (num1, num2) => num1 + num2;

需要注意箭头函数和普通函数的区别

使用字符串模板简化代码

使用模板字符串代替原始的字符串拼接

//Longhandconsole.log('You got a missed call from ' + number + ' at ' + time);//Shorthandconsole.log(`You got a missed call from ${number} at ${time}`);

多行字符串也可使用字符串模板简化

//Longhandconsole.log('JavaScript, often abbreviated as JS, is a\n' +             'programming language that conforms to the \n' +             'ECMAScript specification. JavaScript is high-level,\n' +             'often just-in-time compiled, and multi-paradigm.'            );//Shorthandconsole.log(`JavaScript, often abbreviated as JS, is a            programming language that conforms to the            ECMAScript specification. JavaScript is high-level,            often just-in-time compiled, and multi-paradigm.`            );

对于多值匹配，可将所有值放在数组中，通过数组方法来简写

//Longhandif (value === 1 || value === 'one' || value === 2 || value === 'two') {  // Execute some code}// Shorthand 1if ([1, 'one', 2, 'two'].indexOf(value) >= 0) {   // Execute some code}// Shorthand 2if ([1, 'one', 2, 'two'].includes(value)) {     // Execute some code }

巧用ES6对象的简洁语法

例如，当属性名和变量名相同时，可直接缩写为一个

let firstname = 'Amitav';let lastname = 'Mishra';//Longhandlet obj = {firstname: firstname, lastname: lastname};//Shorthandlet obj = {firstname, lastname};

使用一元运算符简化字符串转数字

//Longhandlet total = parseInt('453');let average = parseFloat('42.6');//Shorthandlet total = +'453';let average = +'42.6';

使用repeat()方法简化重复一个字符串

//Longhandlet str = '';for(let i = 0; i < 5; i ++) {  str += 'Hello ';}console.log(str); // Hello Hello Hello Hello Hello// Shorthand'Hello '.repeat(5);// 想跟你说100声抱歉！'sorry\n'.repeat(100);

使用双星号代替Math.pow()

//Longhandconst power = Math.pow(4, 3); // 64// Shorthandconst power = 4**3; // 64

使用双波浪线运算符（~~）代替Math.floor()

//Longhandconst floor = Math.floor(6.8); // 6// Shorthandconst floor = ~~6.8; // 6

需要注意，~~仅适用于小于2147483647的数字

巧用扩展操作符（...）简化代码

简化数组合并

let arr1 = [20, 30];//Longhandlet arr2 = arr1.concat([60, 80]); // [20, 30, 60, 80]//Shorthandlet arr2 = [...arr1, 60, 80]; // [20, 30, 60, 80]

单层对象的拷贝

let obj = {x: 20, y: {z: 30}};//Longhandconst makeDeepClone = (obj) => {  let newObject = {};  Object.keys(obj).map(key => {      if(typeof obj[key] === 'object'){          newObject[key] = makeDeepClone(obj[key]);      } else {          newObject[key] = obj[key];      }});return newObject;}const cloneObj = makeDeepClone(obj);//Shorthandconst cloneObj = JSON.parse(JSON.stringify(obj));//Shorthand for single level objectlet obj = {x: 20, y: 'hello'};const cloneObj = {...obj};

寻找数组中的最大和最小值

// Shorthandconst arr = [2, 8, 15, 4];Math.max(...arr); // 15Math.min(...arr); // 2

使用for in和for of来简化普通for循环

let arr = [10, 20, 30, 40];//Longhandfor (let i = 0; i < arr.length; i++) {  console.log(arr[i]);}//Shorthand//for of loopfor (const val of arr) {  console.log(val);}//for in loopfor (const index in arr) {  console.log(arr[index]);}

简化获取字符串中的某个字符

let str = 'jscurious.com';//Longhandstr.charAt(2); // c//Shorthandstr[2]; // c

移除对象属性

let obj = {x: 45, y: 72, z: 68, p: 98};// Longhanddelete obj.x;delete obj.p;console.log(obj); // {y: 72, z: 68}// Shorthandlet {x, p, ...newObj} = obj;console.log(newObj); // {y: 72, z: 68}

使用arr.filter(Boolean)过滤掉数组成员的值falsey

let arr = [12, null, 0, 'xyz', null, -25, NaN, '', undefined, 0.5, false];//Longhandlet filterArray = arr.filter(function(value) {    if(value) return value;});// filterArray = [12, "xyz", -25, 0.5]// Shorthandlet filterArray = arr.filter(Boolean);// filterArray = [12, "xyz", -25, 0.5]

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