20个常用的JavaScript简写技巧
作者 | Amitav Mishra
译者 | 清风依旧
策划 | 田晓旭
本文发布在 jscurious.com
//Longhand
let x;
let y = 20;
//Shorthand
let x, y = 20;
//Longhand
let a, b, c;
a = 5;
b = 8;
c = 12;
//Shorthand
let [a, b, c] = [5, 8, 12];
//Longhand
let marks = 26;
let result;
if(marks >= 30){
result = Pass ;
}else{
result = Fail ;
}
//Shorthand
let result = marks >= 30 ? Pass : Fail ;
//Longhand
let imagePath;
let path = getImagePath();
if(path !== null && path !== undefined && path !== ) {
imagePath = path;
} else {
imagePath = default.jpg ;
}
//Shorthand
let imagePath = getImagePath() || default.jpg ;
与 (&&)短路形式书写。//Longhand
if (isLoggedin) {
goToHomepage();
}
//Shorthand
isLoggedin && goToHomepage();
与 (&&)短路写法比较有用。例如：
let x = Hello , y = 55;
//Longhand
const temp = x;
x = y;
y = temp;
//Shorthand
[x, y] = [y, x];
//Longhand
function add(num1, num2) {
return num1 + num2;
}
//Shorthand
const add = (num1, num2) => num1 + num2;
//Longhand
console.log( You got a missed call from + number + at + time);
//Shorthand
console.log(`You got a missed call from ${number} at ${time}`);
//Longhand
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. );
//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.`);
indexOf()或includes()方法。//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
}
let firstname = Amitav ;
let lastname = Mishra ;
//Longhand
let obj = {firstname: firstname, lastname: lastname};
//Shorthand
let obj = {firstname, lastname};
parseInt和parseFloat可以用来将字符串转为数字。我们还可以简单地在字符串前提供一个一元运算符 (+) 来实现这一点。//Longhand
let total = parseInt( 453 );
let average = parseFloat( 42.6 );
//Shorthand
let total = + 453 ;
let average = + 42.6 ;
for循环。但是使用repeat()方法，我们可以一行代码就搞定。//Longhand
let str = ;
for(let i = 0; i < 5; i ++) {
str += Hello ;
}
console.log(str); // Hello Hello Hello Hello Hello
// Shorthand
Hello .repeat(5);
sorry
.repeat(100);
Math.pow()方法来得到一个数字的幂。有一种更短的语法来实现，即双星号 (**)。//Longhand
const power = Math.pow(4, 3); // 64
// Shorthand
const power = 4**3; // 64
Math.floor()方法的缩写。//Longhand
const floor = Math.floor(6.8); // 6
// Shorthand
const floor = ~~6.8; // 6
来自 Caleb 的评论的改进： 双非位运算符只对 32 位整数有效，例如 (2**31)-1 = 2147483647。所以对于任何大于 2147483647 的数字，双非位运算符 (~~) 都会给出错误的结果，这种情况下推荐使用 Math.floor() 方法。
// Shorthand
const arr = [2, 8, 15, 4];
Math.max(...arr); // 15
Math.min(...arr); // 2
for循环。我们可以使用for...of来遍历数组。为了获取每个值的索引，我们可以使用for...in循环。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]);
}
for...in循环来遍历对象属性。let obj = {x: 20, y: 50};
for (const key in obj) {
console.log(obj[key]);
}
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]
JSON.stringify()和JSON.parse()，如果我们的对象不包含函数、undefined、NaN 或日期值的话。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};
来自评论的改进：如果你的对象包含 function, undefined or NaN 值的话，JSON.parse(JSON.stringify(obj)) 就不会有效。因为当你 JSON.stringify 对象的时候，包含 function, undefined or NaN 值的属性会从对象中移除。因此，当你的对象只包含字符串和数字值时，可以使用 JSON.parse(JSON.stringify(obj))。
let str = jscurious.com ;
//Longhand
str.charAt(2); // c
//Shorthand
str[2]; // c
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