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]【相關推薦：javascript學習教程】
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