這篇文章為大家整理分享了20個提升效率的JavaScript簡寫技巧,希望對大家有幫助。
簡寫技巧
#當同時宣告多個變數時,可簡寫成一行
//Longhand let x; let y = 20; //Shorthand let x, y = 20;
利用解構,可為多個變數同時賦值
//Longhand let a, b, c; a = 5; b = 8; c = 12; //Shorthand let [a, b, c] = [5, 8, 12];
巧用三元運算子簡化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||運算子給變數指定預設值
本質是利用了||運算子的特點,當前面的表達式的結果轉成布林值為false時,則值為後面表達式的結果
//Longhand let imagePath; let path = getImagePath(); if (path !== null && path !== undefined && path !== '') { imagePath = path; } else { imagePath = 'default.jpg'; } //Shorthand let imagePath = getImagePath() || 'default.jpg';
使用&&運算子簡化if語句
例如某個函數在某個條件為真時才調用,可簡寫
//Longhand if (isLoggedin) { goToHomepage(); } //Shorthand isLoggedin && goToHomepage();
使用解構交換兩個變數的值
let x = 'Hello', y = 55; //Longhand const temp = x; x = y; y = temp; //Shorthand [x, y] = [y, x];
適用箭頭函數簡化函數
//Longhand function add(num1, num2) { return num1 + num2; } //Shorthand const add = (num1, num2) => num1 + num2;
需要注意箭頭函數和普通函數的區別
使用字串模板簡化程式碼
使用模板字串代替原始的字串拼接
//Longhand console.log('You got a missed call from ' + number + ' at ' + time); //Shorthand console.log(`You got a missed call from ${number} at ${time}`);
多行字串也可使用字串模板簡化
//Longhand console.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.' ); //Shorthand console.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.` );
對於多值匹配,可將所有值放在數組中,透過數組方法來簡寫
//Longhand if (value === 1 || value === 'one' || value === 2 || value === 'two') { // Execute some code } // Shorthand 1 if ([1, 'one', 2, 'two'].indexOf(value) >= 0) { // Execute some code } // Shorthand 2 if ([1, 'one', 2, 'two'].includes(value)) { // Execute some code }
巧用ES6對象的簡潔語法
例如,當屬性名稱和變數名稱相同時,可直接縮寫為一個
let firstname = 'Amitav'; let lastname = 'Mishra'; //Longhand let obj = {firstname: firstname, lastname: lastname}; //Shorthand let obj = {firstname, lastname};
使用一元運算子簡化字串轉數字
//Longhand let total = parseInt('453'); let average = parseFloat('42.6'); //Shorthand let total = +'453'; let average = +'42.6';
使用repeat()方法簡化重複一個字串
//Longhand let 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);
使用雙星號代替Math.pow()
//Longhand const power = Math.pow(4, 3); // 64 // Shorthand const power = 4**3; // 64
使用雙波線運算子(~~)取代Math.floor()
//Longhand const floor = Math.floor(6.8); // 6 // Shorthand const floor = ~~6.8; // 6
需要注意,~~僅適用於小於2147483647的數字
巧用擴充運算子(...)簡化程式碼
簡化數組合併
let arr1 = [20, 30]; //Longhand let arr2 = arr1.concat([60, 80]); // [20, 30, 60, 80] //Shorthand let arr2 = [...arr1, 60, 80]; // [20, 30, 60, 80]
單層物件的拷貝
let obj = {x: 20, y: {z: 30}}; //Longhand const 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); //Shorthand const cloneObj = JSON.parse(JSON.stringify(obj)); //Shorthand for single level object let obj = {x: 20, y: 'hello'}; const cloneObj = {...obj};
尋找陣列中的最大和最小值
// Shorthand const arr = [2, 8, 15, 4]; Math.max(...arr); // 15 Math.min(...arr); // 2
使用for in和for of來簡化普通for迴圈
let arr = [10, 20, 30, 40]; //Longhand for (let i = 0; i < arr.length; i++) { console.log(arr[i]); } //Shorthand //for of loop for (const val of arr) { console.log(val); } //for in loop for (const index in arr) { console.log(arr[index]); }
簡化取得字串中的某個字元
let str = 'jscurious.com'; //Longhand str.charAt(2); // c //Shorthand str[2]; // c
移除物件屬性
let obj = {x: 45, y: 72, z: 68, p: 98}; // Longhand delete obj.x; delete obj.p; console.log(obj); // {y: 72, z: 68} // Shorthand let {x, p, ...newObj} = obj; console.log(newObj); // {y: 72, z: 68}
使用arr.filter(Boolean)過濾掉陣列成員的值falsey
let arr = [12, null, 0, 'xyz', null, -25, NaN, '', undefined, 0.5, false]; //Longhand let filterArray = arr.filter(function(value) { if(value) return value; }); // filterArray = [12, "xyz", -25, 0.5] // Shorthand let filterArray = arr.filter(Boolean); // filterArray = [12, "xyz", -25, 0.5]
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