label)

1.语句

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
</head>
<body>

//if else语句

<button onclick="datenow()">press this button.</button>
<p id="demo"></p>

<script>
function datenow(){
    var x=" "
    var y=" "
    var hours= new Date().getHours();   //定义具体时间，下面依次
    var minutes=new Date().getMinutes();
    var seconds= new Date().getSeconds()

if(hours<16){
    x = hours;
}
else if(hours==16)
{
    x = "it is" + hours;
}
else
{
    y = minutes + " " + seconds;
}
    document.getElementById("demo").innerHTML=x + " " + y;
}

    function star(num){
        num = num || 8                  //当num有值时，取给定的值，否知就为5
//        if (num == undefined){            //没有值时即为undefined
//            num = 8;
//        }
        for (let i = 0; i < num; i++){
            document.write("*")
        }
    }
    star();

//switch语句

<button onclick="datenow()">press this button.</button>
<p id="demo"></p>
<script>
function datenow(){
    var x=" "
    var day = new Date().getDay()
    switch(day){
    case 1:
        x = "monday";           //day变量依次匹配1,2,3的值,即(day===1)恒等式，匹配成功则执行。break停止循环.
        break;                 //中断case
    case 2:
        x = "tuesday";
        break;
    case 3:
        x = "fursday";           //若无break，各个case会依次往下执行
    case 4:                      //case 4和default公用一个命令x = “yours wishes”
    default:
        x = "yours wishes"
    }
    document.getElementById("demo").innerHTML=x;
}

<script>
    function message(age){
        let msg = ''
        switch (true) {
            case age > 50:
                msg = "it is old";
                break;
            case age > 30:
                msg = "it is young";
                break;
            case age > 20:
                msg = "it is younger"
        }
        return msg;
    }
    console.log(message(345));      //输出日志，F12——》console查看返回值
</script>

//for循环遍历

<button onclick="datenow()">press this button.</button>
<p id="demo"></p>
<script>
function datenow(){
    var x;
    var txt="";
    var person={fname:"Bill",lname:"Gates",age:56};
    for(i in person){
        txt = txt + i + "<br>";
        txt = txt + person[i] + "<br>";
    }
    document.getElementById("demo").innerHTML=txt;
}
</script>

<script>
"use strict"                      //严格模式，从当前作用域向下查找（标准化）
cars=["BMW","Volvo","Saab","Ford"];
for(i=0;i<5;i++){
	if(i == 2){
	   continue;        //跳出本次循环，继续后面操作
	}
        if(i == 3){
            break;         //跳出所有循环
        }
	document.write(cars[i] + "<br>");
}
</script>

<script>
    let name = [
        {title: "first name", age: 34},
        {title: "second name", age: 45},
        {title: "third name", age: 56}
    ];                                       //定义变量
    document.write(`
      <table border="1" width="50%">
        <thread><tr><th>Usernames</th><th>Ages</th></tr></thread>
    `)                                      //打印表格并按列在首行依次输入指定内容<th>sss</th>
    for (let i in name) {
        document.write(
            `<tr><td>${name[i].title}</td>  <td>${name[i].age}</td></tr>`
        );                                   //按行从上到下输入各列的内容，空格值有一个生效，多余的不显示
        document.write('<br/>');             //换行
    }
    document.write("</table>")；            //表格结尾
    for (let j of name){
        document.write(j.title);            //for in表示的是键（key），for of表示的是指（value），和Python 的for应用相似
        document。write(`${j.title} is good `); //空格只有一个生效，多余的空格没有作用（建议用法）
        document.write("</br>")               //打印换行
    }

//标签

<script>
outerloop:
for (var i = 0; i < 10; i++)

{
    innerloop:
    for (var j = 0; j < 10; j++)
    {
        if (j > 3)
        {
            break;
        }
        if (i == 2)
        {
            break innerloop;        //退出标签指定的内部for循环
        }
        if (i == 4)
        {
            break outerloop;      //退出标签指定的整个for循环（可用于子层循环退出外层循环）
        }
        document.write("i=" + i + " j=" + j + "<br>");
    }
}
</script>

<script>
    let arr = [10,20,30,40,50]
    for(i=0;i<arr.length;i++){
        document.write(arr[i])
        document.write("<br>")
    }

    for(let j=0; j<arr.length; j++){
        arr[j] = arr[j] + '老狗'
    }
    let m = arr.length
    for(let n=0; n < m; n++){
        arr.push('last',n)              //在数组后面依次添加last+${n}
        arr.unshift('fornt',n)        //在数组前面依次添加front+${n}
    }
    document.write(arr)
    console.log(arr)
    
打印结果：fornt,4,fornt,3,fornt,2,fornt,1,fornt,0,10老狗,20老狗,30老狗,40老狗,50老狗,last,0,last,1,last,2,last,3,last,4

</body>
</html>

posted @ 2022-09-15 15:42 JASON_yul 阅读(55) 评论(0) 收藏举报

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