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1、javascript变量、函数的定义

<script type="text/javascript">
    //var变量声明
    var a=11;
    //输出变量
    console.log(a);
    alert('22');
    //函数定义
    function fun(){
        console.log('33');
    }
    //函数调用
    fun();
</script>

2、javascript流程控制if else switch

<script type="text/javascript">
    //流程控制 if
    function f1(){
        var int=100;
        if (int>100 || int<0) {
            alert('非法值！！！');
        }else if (int>90) {
            alert('优秀！');
        }else if (int<=90 && int>70) {
            alert('及格');
        }else{
            alert('没及格，挨打');
        }
    }
    //流程控制 switch
    function f2() {
        var int=99;
        switch(true){
            case(int >100 || int < 0):
                alert('非法值！');
                break;
            case(int>=90):
                alert('优秀了！');
                break;
            case(int>=70):
                alert('及格了！');
                break;
            default:
                alert('挨打了！');
        }
    }
    //流程控制 if优化
    function f3(){
        var int=80;
        if (int >100 || int < 0) {
            alert('非法值');
        }
        if (int>=90 && int <= 100 ) {
            alert('优秀');
        }
        if (int<=90 && int>=70) {
            alert('及格');
        }
        if (int<70) {
            alert('没过')
        }
    }
    f3();
</script>

3、javascript三种循环

<script type="text/javascript">
//循环 for
function x1(){
    for (var i = 1; i <=10; i++) {
        console.log(i);
    }
}
//循环 while
function x2() {
    var i=10;
    while(i<=100){
        console.log(i);
        i+=10;
    }
}
//循环 do while
function x3() {
    var i=2;
    do{
        console.log(i);
        i+=2;
    }while (i<=20);
}
x3();
</script>

4、数据类型转换：parseInt、isNaN函数的使用

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title></title>
</head>
<body>
<input type="text" name="" id="age" placeholder="输入您的年龄">
<button onclick="age();">提交</button>
<script type="text/javascript">
    function age() {
        var age=document.getElementById('age').value;
        //通过parseInt()函数把age强制转换成整数
        age = parseInt(age);
        //isNaN判断值是否为NaN
        if (isNaN(age)) {
            return alert('年龄值不合法！');
        }
        if (age>120 || age<0) {
            return alert('年龄超过可提交范围，请核实');
        }
        return alert('您的年龄为：'+age);
    }
</script>
</body>
</html>

5、总结

1.NaN 属性是代表非数字值的特殊值，该属性用于指示某个值不是数字。
2.parseInt() 函数可解析一个字符串，并返回一个整数。
3.typeof()函数可以判断变量类型。
4.undefined未定义的变量的数据类型。

Correction status：Uncorrected

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1、javascript变量、函数的定义

2、javascript流程控制if else switch

3、javascript三种循环

4、数据类型转换：parseInt、isNaN函数的使用

5、总结