JS笔记

最新推荐文章于 2025-02-18 17:52:54 发布

q493383189

最新推荐文章于 2025-02-18 17:52:54 发布

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CC 4.0 BY-SA版权

本文链接：https://blog.youkuaiyun.com/q493383189/article/details/72230484

本文深入讲解了JavaScript的基础语法，包括变量声明、数据类型转换、数组操作、字符串处理、条件判断及循环控制等核心内容。

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<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>JS</title>
    <!--引入JS文件-->
    <script src="commons.js"></script>
    <!--JS代码位置-->
    <script>
//        全局变量
        name = 'chenlong';
//        局部变量
        var age = 18;
       function f1() {
            alert('f1');

        }


        /*


        多行注释
         */

        //数字 字符串 数组

//        数字
        var age = 18;
//        var age = Number(18);
//        通过console输出
//
        console.log(age, typeof age);

//        将字符串转化为数字
        nd = parseInt('18');
        console.log(nd, typeof nd);


        Number('123');
        parseInt('123');


        var num02 = '67.5';
        console.log(parseInt(num02));
//        输出67
        console.log(parseFloat(num02));
//        输出67.5
        f1();
        f2();

        var a1 = 1, a2 = 2, a3 = 3;
   </script>


</head>
<body>




    <!--JS建议放在页面底部-->
    <script></script>

</body>
</html>

<!--JS字符串笔记-->
<script>

    name="chen    ";
//"chen    "
name.trimRight();
//"chen"
name.charAt(0);
//"c"
bea="AsLongAsYou";
//"AsLongAsYou"
bea.substring(0,6);
//"AsLong"
bea.indexOf("L");
//2
bea.length;
//11
</script>

布尔值
Boolean(1)
true
Boolean(0)
false
var a = true;
undefined
a
true
Boolean(a)
true

数组
var li=[11,22,33]
undefined
li
(3) [11, 22, 33]
var li2=Array(44,55,66)
undefined
li2
(3) [44, 55, 66]
数组 添加
li.push(44)
4
li
(4) [11, 22, 33, 44]

数组 添加
li.unshift("oo")
5
li
(5) ["oo", 11, 22, 33, 44]
li.splice(3,0,"Chen")
[]
li
(6) ["oo", 11, 22, "Chen", 33, 44]
数组 移除
i =  li.pop()
44
li
(5) ["oo", 11, 22, "Chen", 33]
li.shift()
"oo"
li
(4) [11, 22, "Chen", 33]

数组 切片
li.splice(1,1)
[22]
li.splice(1,2)
(2) ["Chen", 33]
li
[11]
li=[11,22,33,44]
(4) [11, 22, 33, 44]
li.slice(0,2)
(2) [11, 22]
li=[11,22,33,44]
(4) [11, 22, 33, 44]
n=["chenlong"]
["chenlong"]
数组 组合
m =   li.concat(n)
(5) [11, 22, 33, 44, "chenlong"]
m
(5) [11, 22, 33, 44, "chenlong"]
li
(4) [11, 22, 33, 44]
m
(5) [11, 22, 33, 44, "chenlong"]

数组 符号连接
c=m.join('-')
"11-22-33-44-chenlong"
c
"11-22-33-44-chenlong"
长度
c.length
20
字典
dic = {"k1":"v1"}
Object {k1: "v1"}
dic
Object {k1: "v1"}


JSON 序列化

dic = {"k1":"v1"}
Object {k1: "v1"}
s = JSON.stringify(dic)
"{"k1":"v1"}"

JSON 反序列化
m = JSON.parse(s)
Object {k1: "v1"}
m
Object {k1: "v1"}

数值 undefined
var chenl;
undefined
数值 null
null
null
chenl = null
null
chenl
null
Boolean(chenl)
false
Boolean(undefined)
false
数组 for循环下标
var gnames=["liu", "li", "lu", "lo"]
undefined
for(var i in gnames){
    console.log(i)
}
VM287:2 0
VM287:2 1
VM287:2 2
VM287:2 3
undefined

字典for循环
var dic = {"k1":11, "k2":22};
undefined
for(var it in dic){
    console.log(it)
}
VM392:2 k1
VM392:2 k2
undefined

FOR循环
for(var i=0;i<5;i++){
    console.log(i);
}
VM439:2 0
VM439:2 1
VM439:2 2
VM439:2 3
VM439:2 4
undefined
FOR循环 循环输出数组
for(var i=0;i<gnames.length;i++){
    console.log(gnames[i]);
}
VM486:2 liu
VM486:2 li
VM486:2 lu
VM486:2 lo
undefined


while循环
while(true){
    continue;
    break;
}

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>JS Prac</title>
</head>
<body>
    <script>
//        while循环
        count = 0;
        while (count < 5){
            console.log(count);
            count++;
            continue;
//            break;
        }

//        IF判断
        var t = 5;
        if(t==4) {
            console.log(t);
            console.log('hi');
        }else if(t == 5){
            console.log(t);
            console.log('hi2');
        }else{
            console.log('mmp')
        }

//        switch选择逻辑
        var ch=2;
        switch (ch){
            case 1:
                console.log('bi');
                break;
            case 2:
                console.log('ng');
                break;
            default:
                console.log('o!')
        }
//        异常处理
        try{

        }catch (e){

        }finally {

        }
//        函数
        function func2(arg) {
            console.log(arg);
            return "chenlong";
        }

        var ret = func2(123)
        console.log(ret)
//        匿名函数

        var f = function (arg) {
            console.log(arg);
        };
        f(9998);
//        自执行函数
        (function(arg2){
            console.log(arg2);
        })("Ivien");

//        面向对象、类
        function Foo(name, age) {
            this.Name = name;
            this.Age = age;
            this.Func = function (arg) {
                return this.Name + arg
            }
        }

        var obj = new Foo("Liu", 27);
        console.log(obj.Name);
        console.log(obj.Age);
        var ret = obj.Func("Lulu");
        console.log(ret)

    </script>
</body>
</html>