20个JS简写技巧提升工作效率

前言：

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

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]

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