将参数添加到原数组末尾，并返回数组的长度

将参数添加到原数组开头，并返回数组的长度

if(){

}else if(){

}else{

}

for(var i = 0; i< 10; i++){
if(i==10) {
break; 中止循环
}
if(i==5) {
continue; 跳出本次循环
}
}

document.getElementById("demo")

console.log('hello word');

while (条件)
{
需要执行的代码
}

do
{
x=x + "The number is " + i + "
";
i++;
}
while (i<5);

setInterval(function(){alert("Hello")},3000);

document.getElementByTagName("div")

document.getElementByClassName("header")

obj.getAttrbute("title")

obj.setAttrbute("title","流星雨")

element.childNodes

document.body.nodeType

childNodes[0].nodeValue

childNodes[0].nodeValue == childNodes.firstChild.nodeValue

node.lastChild

let foo = ["a","b","c"]

let [a,b] = foo; // a = "a" ; b = "b"

class A{
constructor(name,age){
this.name = name;
this.age = age
}
}

//
class B extends A{
constructor(){
// 子类必须在constructor 中指定super 函数
// 如果没有置顶constructor 默认带super的函数的constructor 将会被添加
super("lxy",25)
}
}

export const a = "123"


export default {

}

import A from "a" // a.js

let c = "c"

let b = `ab ${a}` // abc

const a = "a"
const b = "b"

const c = {
a:a
b:b
}

// 简写

const c = {
a,
b
}

let req = new Promise((resolve,reject)=>{
setTimeout(resolve,1000)
})

req.then(res => {
console.log(res)
})

if(arr.includes(x)){

}

async login(){
const user = await get_user();
}

this.login();

const obj = {a:1,b:2,c:3}

console.log(Object.values(obj1)); // [1,2,3]

for (let [key,value] of Object.entires(obj)){
console.log(`key:${key},value:${value}`)
}