循环语句

循环语句有while、do…while 、for 、for…in 下面简单的介绍一下使用方法

1.while

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8" />
        <title></title>
    </head>
    <body>
        <script type="text/javascript">
            var num1=1;
            while(num1 < 10){
                console.log((num1));
                num1++;
            }
        </script>
    </body>
</html>

运行结果：
在这里插入图片描述

2.do…while

do…while循环与while循环有一些区别，while循环先判断在循环而do…while循环是先执行一次在判断，注意这个区别。

```javascript
<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8" />
        <title></title>
    </head>
    <body>
        <script type="text/javascript">
            var num1=1;
            do{
                console.log("Hello");
            } while(num1>2)
        </script>
    </body>
</html>
<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8" />
        <title></title>
    </head>
    <body>
        <script type="text/javascript">
            var num1=1;
            while(num1 > 2){
                console.log("Hello");
            }
        </script>
    </body>
</html>

运行结果：
在这里插入图片描述

3.for

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8" />
        <title></title>
    </head>
    <body>
        <script type="text/javascript">
            var num1=10;
            for(var i = 0; i < num1; i++){
                console.log(i);
            }
        </script>
    </body>
</html>

运行结果：
在这里插入图片描述

4.for…in

for…in语句主要用于数组。

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8" />
        <title></title>
    </head>
    <body>
        <script type="text/javascript">
            var arr = ["a","b","c","d"];
            for(var i in arr){
                console.log(arr[i]);
            }
        </script>
    </body>
</html>