终生能用的JS代码优化

多个if 语句 => 把多个值放在一个数组中，然后调用数组的 includes 方法。

//longhand
if (x === 'abc' || x === 'def' || x === 'ghi' || x ==='jkl') {
    //logic
}
//shorthand
if (['abc', 'def', 'ghi', 'jkl'].includes(x)) {
   //logic
}

if-else 条件 => 三元运算符来实现这种简化

// Longhand
let test: boolean;
if (x > 100) {
    test = true;
} else {
    test = false;
}
// Shorthand
let test = (x > 10) ? true : false;
//or we can use directly
let test = x > 10;
console.log(test);

变量声明

//Longhand 
let test1;
let test2 = 1;
//Shorthand 
let test1, test2 = 1;

null、undefined 和空值检查

// Longhand
if (test1 !== null || test1 !== undefined || test1 !== '') {
    let test2 = test1;
}
// Shorthand
let test2 = test1 || '';

给多个变量赋值

//Longhand 
let test1, test2, test3;
test1 = 1;
test2 = 2;
test3 = 3;
//Shorthand 
let [test1, test2, test3] = [1, 2, 3];

简便的赋值操作符

// Longhand
test1 = test1 + 1;
test2 = test2 - 1;
test3 = test3 * 20;
// Shorthand
test1++;
test2--;
test3 *= 20;

if 判断值是否存在

// Longhand
if (test1 === true) or if (test1 !== "") or if (test1 !== null)
// Shorthand //it will check empty string,null and undefined too
if (test1)

用于多个条件判断的 && 操作符

//Longhand 
if (test1) {
 callMethod(); 
} 
//Shorthand 
test1 && callMethod();

箭头函数

//Longhand 
function add(a, b) { 
   return a + b; 
} 
//Shorthand 
const add = (a, b) => a + b;


function callMe(name) {
  console.log('Hello', name);
}
callMe = name => console.log('Hello', name);

switch 简化

// Longhand
switch (data) {
  case 1:
    test1();
  break;
  case 2:
    test2();
  break;
  case 3:
    test();
  break;
  // And so on...
}
// Shorthand
var data = {
  1: test1,
  2: test2,
  3: test
};
data[something] && data[something]();

指数表示法

// Longhand
for (var i = 0; i < 10000; i++) { ... }
// Shorthand
for (var i = 0; i < 1e4; i++) {

默认参数值

//Longhand
function add(test1, test2) {
  if (test1 === undefined)
    test1 = 1;
  if (test2 === undefined)
    test2 = 2;
  return test1 + test2;
}
//shorthand
add = (test1 = 1, test2 = 2) => (test1 + test2);
add() //output: 3

延展操作符简化

//longhand
// joining arrays using concat
const data = [1, 2, 3];
const test = [4 ,5 , 6].concat(data);
//shorthand
// joining arrays
const data = [1, 2, 3];
const test = [4 ,5 , 6, ...data];
console.log(test); // [ 4, 5, 6, 1, 2, 3]

模板字面量

//longhand
const welcome = 'Hi ' + test1 + ' ' + test2 + '.'
//shorthand
const welcome = `Hi ${test1} ${test2}`;

将字符串转成数字

//Longhand 
let test1 = parseInt('123'); 
let test2 = parseFloat('12.3'); 
//Shorthand 
let test1 = +'123'; 
let test2 = +'12.3';

变量解构

//longhand
const test1 = this.data.test1;
const test2 = this.data.test2;
const test2 = this.data.test3;
//shorthand
const { test1, test2, test3 } = this.data;

数组 find 简化

const data = [{
        type: 'test1',
        name: 'abc'
    },
    {
        type: 'test2',
        name: 'cde'
    },
    {
        type: 'test1',
        name: 'fgh'
    },
]
function findtest1(name) {
    for (let i = 0; i < data.length; ++i) {
        if (data[i].type === 'test1' && data[i].name === name) {
            return data[i];
        }
    }
}
//Shorthand
filteredData = data.find(data => data.type === 'test1' && data.name === 'fgh');
console.log(filteredData); // { type: 'test1', name: 'fgh' }

indexOf 的按位操作简化

//longhand
if(arr.indexOf(item) > -1) { // item found 
}
if(arr.indexOf(item) === -1) { // item not found
}
//shorthand
if(~arr.indexOf(item)) { // item found
}
if(!~arr.indexOf(item)) { // item not found
}

双重按位操作

// Longhand
Math.floor(1.9) === 1 // true
// Shorthand
~~1.9 === 1 // true

查找数组的最大值和最小值

const arr = [1, 2, 3]; 
Math.max(…arr); // 3
Math.min(…arr); // 1