JavaScript基本流程控制 if, switch, while, do while, for 

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>

</body>
<style>
    span{
        display: inline-block;
        width: 20px;
        border: 1px solid black;

    }
</style>
<script>
    // If 语句
    if(1){
        console.log(1);
    }else{
        console.log(0);
    }

    if(1){
        console.log(1);
    }else if(1+1 == 3){
        console.log(0);
    }

    // 三元表达式: 条件是否满足？满足输出2，否则输出5
    let hd = true ? 2:5;

    // switch
    let name = "ziwen";
    switch(name){
        case undefined:
            console.warn("undefined!");
        case "":
            console.log('可能是以下值');
        case 'zi':
            console.log('zi');
            break;
        case 'ziwen':
            console.log('ziwen');
            break;
        default:
            console.log("yes");
    }

    // switch 替代 if
    switch(true){
        case 1+1==2:
            console.warn("undefined!");
            break;
        case 0:
            console.log('zi');
            break;
        default:
            console.log("yes");
    }

    // while, do while

    document.write(
        '<table border="1" width="100%">'
    );
    let tr = 5;

    while (tr-- > 0) {
        document.write('<tr>');
        let td = 3;
        do {
            document.write('<td>'+td+'</td>');
        } while (--td > 0);
        document.write('</tr>');
    }
    document.write(
        '</table>'
    );

    // for 打印杨辉三角
    for(let i = 0; i < 4; i++){
        for (let j = 4 - i; j > 0; j--) {
            document.write("<span>*</span>");
        }
        for (let k = 2 * i + 1; k > 0; k--) {
            document.write("<span>&</span>");
        }
        document.write("<br>");
    }

    // for-in
    for (const key in object) {
        if (object.hasOwnProperty(key)) {
            const element = object[key];
            
        }
    }

    // for-of
    for (const iterator of object) {
        // 循环迭代对象：包括数组，字符串
    }

</script>
</html>

 

posted @ 2020-11-27 19:16  SvenWayne  阅读(98)  评论(0)    收藏  举报