常用js小技巧杂记

1.判断是否为空对象

 !Object.keys(obj).length

2.动态属性名

const dynamic = 'email';
let user = {
    name: 'John',
    [dynamic]: 'john@doe.com'
}
console.log(user); // outputs { name: "John", email: "john@doe.com" }

3.数组map的方法

const cities = [
    { name: 'Paris', visited: 'no' },
    { name: 'Lyon', visited: 'no' },
    { name: 'Marseille', visited: 'yes' },
    { name: 'Rome', visited: 'yes' },
    { name: 'Milan', visited: 'no' },
    { name: 'Palermo', visited: 'yes' },
    { name: 'Genoa', visited: 'yes' },
    { name: 'Berlin', visited: 'no' },
    { name: 'Hamburg', visited: 'yes' },
    { name: 'New York', visited: 'yes' }
];

const cityNames = Array.from(cities, ({ name}) => name);
console.log(cityNames);
// outputs ["Paris", "Lyon", "Marseille", "Rome", "Milan", "Palermo", "Genoa", "Berlin", "Hamburg", "New York"]

4.操作URL查询参数

const params = new URLSearchParams(location.search.replace(/\?/ig, "")); // location.search = "?name=yajun&sex=female"
params.has("yajun"); // true
params.get("sex"); // "female"

5.混淆数组

const arr = [0, 1, 2, 3, 4, 5].slice().sort(() => Math.random() - .5);
// arr => [3, 4, 0, 5, 1, 2]

6.删除对象属性

用解构赋值配合 rest 操作符可以删除对象属性。
下面的 password 属性会在解构的时候被忽略，...rest 里其余的属性作为 rest 返回：
const noPassword = ({ password, ...rest }) => rest
const user = {
  id: 100,
  name: 'Howard Moon',
  password: 'Password!'
}
noPassword(user) //=> { id: 100, name: 'Howard moon' }

7.首行缩进两个字符

text-indent: 2em

8.深度拷贝对象

function cloneObj(obj) {
    var o = obj.constructor == Object ? new obj.constructor() : new obj.constructor(obj.valueOf());
    for(var key in obj){
        if(o[key] != obj[key] ){
            if(typeof(obj[key]) == 'object' ){
                o[key] = mods.cloneObj(obj[key]);
            }else{
                o[key] = obj[key];
            }
        }
    }
    return o;
    }

9.判断数组元素是否重复

var isRepeat = function(arr) {  //arr是否有重复元素
    var hash = {};
    for (var i in arr) {
        if (hash[arr[i]]) return true;
        hash[arr[i]] = true;
    }
    return false;
    };