JavaScript

var a = "abcdef";
console.log(a[1]);         # b
a[1] = 'b';                # 这里尝试把'b'赋值给a[1]
                           # 没有显示报错，赋值完成
console.log(a[1])          # a
                           # 发现虽然赋值完成，但值没有改变，赋值失败

var arr01 = [1,2,3,4,5,6,7,8,9]; # 可以通过数组下标进行取值和赋值 
console.log(arr01);              # [1, 2, 3, 4, 5, 6, 7, 8, 9]
arr01[0] = 0;
console.log(arr01);              # 0, 2, 3, 4, 5, 6, 7, 8, 9]

var age = 18;
if(age > 18){
    console.log("成年了");
}else if(age === 18){
    console.log("刚成年");
}else {
    console.log("未成年");
}

var a = 0;
while(a < 100){
    a = a + 1;
    console.log(a);
}
var b = 0;
do{
    b = b + 1;
    console.log(b);
}while(b < 100)

for(let i = 0; i < 100; i++){
    console.log(i);
}

var arr = [1,2,3,4,5,6,7,8,9];

# for(var 下标 in 容器)

for(var num in arr){
    console.log(arr[num]);
}

var map = new Map([["tom",99],["jerry",98],["alice",95],["bob",96]]);
// get方法通过键来找到值
console.log(map.get("tom"));
// set方法添加或者修改键值对
map.set("hhhhh",100);
// delete方法删除键值对
map.delete("tom");

var map = new Map([["tom",99],["jerry",98],["alice",95],["bob",96]]);
for(var x of map){
    console.log(x);
}

var set = new Set([1,2,3,3,3,3,3,3]) 
set.add(2);                          //添加元素
set.delete(1);                       //删除元素
set.has(3);                          //判断是否包含

function MyAbs(x){
    if(x >= 0){
        return x;
    }else{
        return -x;
    }
}

var MyAdd = function(a,b){
    if(arguments.length !== 2){
        throw "Not a Number"
    }
    return a+b;
}

function abbb(a,b,...rest){
    函数体.....
}
abbb(1,2,3,4,5,6,7,8)       # 调用函数，传参
                         # a === 1
                         # b === 2
                         rest = [3,4,5,6,7,8]

var a = 10;
function test() {
    var a = 20;
    console.log(this.a);
    console.log(a);
    console.log("====================");
}
console.log(a);
test();
a = 30;
console.log(a);
test();

let a = 10;
function test() {
    let a = 20;
    console.log(window.a);
    console.log(a);
    console.log("====================");
}
console.log(a);
test();
a = 30;
console.log(a);
test();

var hh = {
       name : "hs",
       ahe : 18,
       birth : 2005,
       // 方法
       age : function(){
           return new Date().getFullYear() - this.birth;
       }
}
// 属性
hh.name;
// 方法
hh.age();

function getAge(){
    return new Date().getFullYear() - this.birth;
}
var hh = {
    name : "hs",
    ahe : 18,
    birth : 2005,
    age : getAge
}

var person = {
            name: "John",
            age: 30,
            city: "New York"
        }
        // 对象转换为JSON字符串
        var json = JSON.stringify(person);
        console.log(json)
        // JSON字符串转换为对象
        var obj =JSON.parse(json);
        console.log(obj)
        // 也可以用 JSON.parse('{"name":"John","age":30,"city":"New York"}')

class person01 {
    constructor(name, age){
    this.name = name;
    this.age = age;
    }
    run() {
        console.log(this.name + " is running");
    }
}
var xiaoming = new person01("xiaoming", 25);
var xiaohong = new person01("xiaohong", 20);

class 子类名 extend 父类名{
    constructor(参数){
        super()
    }
}

class person02 extends person01 {
    constructor(name, age, sex) {
        super(name, age);
        this.sex = sex;
    }
    sayHello() {
        console.log("Hello, my name is " + this.name + " and I am a " + this.sex);
    }
}

window.alert(1)
undefined
window.innerHeight
358
window.innerWidth
1659
window.outerWidth
1707
window.outerWidth
1707

appName    # 浏览器的官方名称。通常是"Netscape"，
           # 这是因为Netscape是第一个支持JavaScript的浏览器。
appVersion # 提供了浏览器版本信息
userAgent  # 浏览器的用户代理字符串
platform   # 运行浏览器的操作系统平台

screen.width
1707 px
screen.height
960 px

host: "ntp.msn.cn"
protocol: "https:"
reload: ƒ reload()    // 刷新网页

document.title
'新建标签页'
document.title = '呵帅'
'呵帅'

// 后退
history.back()
// 前进
history.forward()

<div id="father">
    <h1>标题</h1>
    <p id="p1">段落</p>
    <p class="p2">段落</p>
</div>
<script>
    //对应CSS选择器
    var h1 =document.getElementsByName('h1');
    var p = document.getElementsByName('p');
    var div = document.getElementsByName('div');
    var father = document.getElementById('father');
    var p2 = document.getElementsByClassName('p2');
    var p1 =document.getElementsByTagName('p1')
</script>

<div id="father">
    <h1>标题</h1>
    <p id="p1">段落</p>
    <p class="p2">段落</p>
</div>
<script>
    var p1 = documents.getElementById('p1');
    var father = p1.parentElement;
    father.removeChild(p1)
</script>

<div id="father">
    <h1>标题</h1>
    <p id="p1">段落</p>
    <p class="p2">段落</p>
</div>
<script>
    father.removeChild(father.children[0]);
    father.removeChild(father.children[0]);
    father.removeChild(father.children[0]);
</script>

<p>
    <span>输入内容:</span> <input type="text" id="input">
</p>
<p>
    <span>性别:</span>
    <input type="radio" value="man" name="sex" id="boy"> 男
    <input type="radio" value="woman" name="sex" id="girl"> 女
</p>

<script>
    var input_text = document.getElementById('input');
    var boy_radio = document.getElementById('boy');
    var girl_radio = document.getElementById('girl');
</script>

<p>
    请输入用户名：<input type="text" id="username" name="username" placeholder="请输入用户名">
</p>
<p>
    请输入密码 ：<input type="password" id="password" name="password" placeholder="请输入密码">
</p>
<!--绑定事件 onclick-->
<button type="button" onclick="submit()">提交</button>
<script>
    function submit() {
        var username = document.getElementById("username");
        var password = document.getElementById("password");
        console.log(username.value);
        console.log(password.value);
    }
</script>

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script src="https://cdn.staticfile.org/jquery/1.10.2/jquery.min.js"></script>
    <style>
        #div1 {
            width: 500px;
            height:500px;
            border: 1px solid red;
        }
    </style>
</head>
<body>
    <span id="span1"></span>
    <div id="div1">
        移动区域
    </div>
    <script>
        $(document).ready(function (){
            $("#div1").mousemove(function (e){
                $("#span1").text("x"+e.pageX+"y"+e.pageY);
            })
        })
    </script>
</body>
</html>