提升效率的JS简写技巧

最近看了一些简化 JS 代码的文章，其中有一篇觉得还不错，但是是英文的，也看了一些中文翻译，一个是一字一句翻译太生硬，没有变成自己的东西，另外就是后面作者有新增没有及时更新，于是我按照自己的语言翻译整理成此文，本文特点以言简意赅为主

简写技巧

🍅 当同时声明多个变量时，可简写成一行

//Longhand
let x;
let y = 20;

//Shorthand
let x,
  y = 20;

🍅 利用解构，可为多个变量同时赋值

//Longhand
let a, b, c;

a = 5;
b = 8;
c = 12;

//Shorthand
let [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

//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&&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

//Longhand
if (isLoggedin) {
  goToHomepage();
}

//Shorthand
isLoggedin && goToHomepage();

🍅 使用解构交换两个变量的值

let x = "Hello",
  y = 55;

//Longhand
const temp = x;
x = y;
y = temp;

//Shorthand
[x, y] = [y, x];

🍅 适用箭头函数简化函数

//Longhand
function add(num1, num2) {
  return num1 + num2;
}

//Shorthand
const add = (num1, num2) => num1 + num2;

🍅 使用字符串模板简化代码

//Longhand
console.log("You got a missed call from " + number + " at " + time);

//Shorthand
console.log(`You got a missed call from ${number} at ${time}`);

🍅 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

//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 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";

//Longhand
let obj = { firstname: firstname, lastname: lastname };

//Shorthand
let obj = { firstname, lastname };

🍅 使用一元运算符简化字符串转数字

//Longhand
let total = parseInt("453");
let average = parseFloat("42.6");

//Shorthand
let total = +"453";
let average = +"42.6";

🍅 使用 repeat()方法简化重复一个字符串

//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);

🍅 使用双星号代替 Math.pow()

//Longhand
const power = Math.pow(4, 3); // 64

// Shorthand
const power = 4 ** 3; // 64

🍅 使用双波浪线运算符（~~）代替 Math.floor()

//Longhand
const floor = Math.floor(6.8); // 6

// Shorthand
const floor = ~~6.8; // 6

🍅 巧用扩展操作符（...）简化代码

• 简化数组合并

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]

• 单层对象的拷贝

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 };

• 寻找数组中的最大和最小值

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

🍅 使用 for in 和 for of 来简化普通 for 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]);
}

🍅 简化获取字符串中的某个字

let str = "jscurious.com";

//Longhand
str.charAt(2); // c

//Shorthand
str[2]; // c

🍅 移除对象属性

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)过滤掉数组成员的值 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]