JavaScript基础语法（类型转换）

偏执的太偏执、 2024-03-31 12:55 65阅读 0赞

## JavaScript基础语法（类型转换） ##

**学习路线**：[JavaScript基础语法（输出语句）][JavaScript]\->[JavaScript基础语法（变量）][JavaScript 1]\->[JavaScript基础语法（数据类型）][JavaScript 2]\->[JavaScript基础语法（运算符）][JavaScript 3]\->[JavaScript基础语法（流程控制语句）][JavaScript 4]\->[JavaScript基础语法（类型转换）][JavaScript 5]\->[JavaScript基础语法（函数）][JavaScript 6]\->[Array\_JavaScript][Array_JavaScript]\->[String\_JavaScript][String_JavaScript]\->[自定义对象\_JavaScript][JavaScript 7]\->[JavaScript\_BOM][JavaScript_BOM]\->[Window对象][Window]\->[confirm()、setInterval()、setTimeout()][confirm_setInterval_setTimeout]\->[History、Location][History_Location]\->[闪烁的灯泡][Link 1]\->[JavaScript\_DOM][JavaScript_DOM]\->[事件绑定(onclick,onfocus,onblur)][onclick_onfocus_onblur]\->  
[事件绑定(onmouseout,onmouseover)  
][onmouseout_onmouseover_]\->[事件绑定(onsubmit)表单提交  
][onsubmit_]\->[提交表单与验证表单案例  
][Link 2]  
使用`==`运算符的时候会发生类型转换。

### 其他类型转为number ###

*  `string`转换为 `number`类型：按照字符串的字面值，转为数字。如果字面值不是数字，则转为NaN
    
    将 `string`转换为 `number`有两种方式：
    
     *  使用 `+` 正号运算符：

<!DOCTYPE html>
    <html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>Title</title>
    </head>
    <body>
        
    <script>
        var str = + "20";
        document.write(str + 1) //21
    </script>
    </body>
    </html>

**运行结果**  
![在这里插入图片描述][4506d59f1ac24795822eb9684596d6c1.png]

### 使用 `parseInt()` 函数(方法)： ###

<!DOCTYPE html>
    <html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>Title</title>
    </head>
    <body>
        
    <script>
        var str = "20";
        document.write(parseInt(str) + 1);
    </script>
    </body>
    </html>

**运行结果**  
![在这里插入图片描述][22db028d954d4368b28bb72241bb66a2.png]

*  `boolean`转换为 `number`类型：true 转为1，false转为0

<!DOCTYPE html>
    <html lang="en">
    <head>
      <meta charset="UTF-8">
      <title>Title</title>
    </head>
    <body>
      
    <script>
      var flag = +false;
      document.write(flag); // 0
    </script>
    </body>
    </html>

**运行结果**  
![在这里插入图片描述][bd08dce9acba4ebdb21e3f249a1e1841.png]

### 其他类型转为boolean ###

*  number 类型转换为 boolean 类型：0和NaN转为false，其他的数字转为true
 *  string 类型转换为 boolean 类型：空字符串转为false，其他的字符串转为true
 *  null类型转换为 boolean 类型是 false
 *  undefined 转换为 boolean 类型是 false

[JavaScript]: https://blog.csdn.net/qq_51447496/article/details/128085137
[JavaScript 1]: https://blog.csdn.net/qq_51447496/article/details/128085348
[JavaScript 2]: https://blog.csdn.net/qq_51447496/article/details/128086148
[JavaScript 3]: https://blog.csdn.net/qq_51447496/article/details/128086681
[JavaScript 4]: https://blog.csdn.net/qq_51447496/article/details/128088817
[JavaScript 5]: https://blog.csdn.net/qq_51447496/article/details/128087248
[JavaScript 6]: https://blog.csdn.net/qq_51447496/article/details/128088986
[Array_JavaScript]: https://blog.csdn.net/qq_51447496/article/details/128089474
[String_JavaScript]: https://blog.csdn.net/qq_51447496/article/details/128089631
[JavaScript 7]: https://blog.csdn.net/qq_51447496/article/details/128089766
[JavaScript_BOM]: https://editor.csdn.net/md/?articleId=128095193
[Window]: https://blog.csdn.net/qq_51447496/article/details/128095300
[confirm_setInterval_setTimeout]: https://blog.csdn.net/qq_51447496/article/details/128103458
[History_Location]: https://blog.csdn.net/qq_51447496/article/details/128104240
[Link 1]: https://blog.csdn.net/qq_51447496/article/details/128095524
[JavaScript_DOM]: https://blog.csdn.net/qq_51447496/article/details/128104720
[onclick_onfocus_onblur]: https://blog.csdn.net/qq_51447496/article/details/128110532
[onmouseout_onmouseover_]: https://blog.csdn.net/qq_51447496/article/details/128112439
[onsubmit_]: https://blog.csdn.net/qq_51447496/article/details/128112553
[Link 2]: https://blog.csdn.net/qq_51447496/article/details/128112770
[4506d59f1ac24795822eb9684596d6c1.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/31/ecd9cf1488a24dd1b0372939a8165cee.png
[22db028d954d4368b28bb72241bb66a2.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/31/04f2d8332635438fb3cf7ffe6ea84267.png
[bd08dce9acba4ebdb21e3f249a1e1841.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/31/deb450dbcf814c3782f6ea571b473b1a.png