lovecoding
/
VIPJAVA


			
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							<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>入门</title>
</head>
<body>
<script>
    //弹出框
    //alert("hello js")

    //写入到页面
    //document.write("hello javascript")

    //浏览器控制台 推荐
    console.log("浏览器控制台输出")
    console.log("浏览器控制台输出")

    //变量 全局变量
    var a = 12;

    console.log( typeof a);
    console.log("变量:"+a);

    {
        var b = 22;
    }
    console.log("变量:"+b);

    // {
    //     let c = 30;
    // }
    // console.log("变量:"+c);

    const d = 10;
    console.log("变量:"+d);


    //数据类型
    /*
        5种 number String null boolean undefind
     */
    let n = 20;

    let s = "hello js";

    let m = null;

    let t = true;

    let f ;

    console.log(typeof n)
    console.log(typeof s)
    console.log(typeof m)
    console.log(typeof t)
    console.log(typeof f)

    //转换
    var s1 = "20";
    var s2 = "30abc";

    var a = +"10"+10;

    console.log(s1+a);
    console.log(s2+a);
    console.log(a);

    //方法
    let number = parseInt("a123abc");
    console.log(number)

    //布尔  true 1 false 0
    let b2 = true+1;
    console.log(b2)

    //数字 booelan 0 false 其余 true
    if (3){
        console.log(3)
    }

    //字符串
    if (""){
        console.log("空窜") // false 其余 true
    }


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