提升效率的JS简写技巧，你值得拥有！

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;

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

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

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

多行字符串也可使用字符串模板简化

//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.`
            );

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

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];

//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符

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]