JavaScript学习笔记（01JS基础-P44-P59）

  用法

 数据类型：

 

 

 

 示例代码：

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <title></title>
</head>
<body>
    <script>
        var s = "Hello!";
        var i = 10;
        var b = true;
        var arr = [5, 12, 43, 87.2];
        //document.write(arr[2]);
        //var arr1 = new Array("Heoolpw", "time", "span");
        //第二种方式生成数组
        var arr2 = new Array();
        arr2[0] = "happt";
        arr2[1] = "Hellow";
        arr2[2] = 1;
        arr2[3] = 1000;
        //document.write(arr2[2]);
        var n = null;//空
        var und;//未定义
        document.write(n);//输出 null
    </script>
</body>
</html>
View Code

JS中的运算符

 

 

 条件语句

 

 

 

if else

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <title></title>
</head>
<body>
    <script>
        var u = 10;
        if (u > 10) {
            document.write("u大于10");
        }
        else if (u < 10) {
            document.write("u小于于10");
        }
        else {
            document.write("u等于10");
        }
    </script>
</body>
</html>
View Code

 

switch

 

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <title></title>
</head>
<body>
    <script>
        var i = "Hellow";
        switch (i) {
            case "Hellow":
                document.write("Hellow");
                break;
            case "Time":
                document.write("Time");
                break;
            default:
                document.write("default");
                break;
        }
    </script>
</body>
</html>
View Code

 

 

 

 

for 和for in循环：

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <title></title>
</head>
<body>
    <script>
        var arr = [1, 2, 3, 4, 5, 6, 7];
        for (var i = 0; i < arr.length; i++) {
            document.write(arr[i]);
            document.write("<br/>");
        }
        for (var i in arr) {
            document.write(arr[i] + "、");//注意for in的用法，i只是下标
        }
    </script>
</body>
</html>
View Code

 

while和do-while循环：

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <title></title>
</head>
<body>
    <script>
        var i = 0;
        while (i < 10) {
            document.write(i + "<br/>");
            i++;
        }
        var j = 0;
        do {
            document.write(j);
            j++;
        } while (j<10);
    </script>  
</body>
</html>
View Code

 

 

 

 

函数:

 

 

 

函数调用

 

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <title></title>
</head>
<body>
    <script>
        function myfunction(a,b) {
            var sum = a + b;
            alert(sum);
            return sum;           
        }
        //方式一：在script标签内调用
        var sum = myfunction(10, 40);       
    </script>
    <!--方式二：在HTML中调用-->
    <input type="button" value="按钮" onclick="myfunction(20,50)" />
   
</body>
</html>
View Code

 

 

 

 

 

 

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <title></title>
</head>
<body>
    <script>
        var n = 50;//全局变量，都可以使用
        m = 300;//全局变量，都可以使用
        function demo() {
            var i = 100;//局部变量，只能在该代码块内使用
            x = 20;//注意 全局变量，该函数调用后，全局都可以使用
        }
    </script>
</body>
</html>
View Code

 

End

posted @ 2020-02-07 16:26  ZedFFF  阅读(148)  评论(0)    收藏  举报