JavaScript 字符串和数字转换

问题描述

如何在 JavaScript 中执行以下操作?

How can I do the following in JavaScript?

1. 将1"、2"、3"连接成123"

1. Concatenate "1", "2", "3" into "123"

将123"转换为123

Convert "123" into 123

加 123 + 100 = 223

Add 123 + 100 = 223

将223转换为223"

Covert 223 into "223"

推荐答案

你想熟悉 parseInt() 和 toString().

在您的工具包中有用的是查看变量以找出它是什么类型—typeof:

And useful in your toolkit will be to look at a variable to find out what type it is—typeof:

<script type="text/javascript">
    /**
     * print out the value and the type of the variable passed in
     */

    function printWithType(val) {
        document.write('<pre>');
        document.write(val);
        document.write(' ');
        document.writeln(typeof val);
        document.write('</pre>');
    }

    var a = "1", b = "2", c = "3", result;

    // Step (1) Concatenate "1", "2", "3" into "123"
    // - concatenation operator is just "+", as long
    //   as all the items are strings, this works
    result = a + b + c;
    printWithType(result); //123 string

    // - If they were not strings you could do
    result = a.toString() + b.toString() + c.toString();
    printWithType(result); // 123 string

    // Step (2) Convert "123" into 123
    result = parseInt(result,10);
    printWithType(result); // 123 number

    // Step (3) Add 123 + 100 = 223
    result = result + 100;
    printWithType(result); // 223 number

    // Step (4) Convert 223 into "223"
    result = result.toString(); //
    printWithType(result); // 223 string

    // If you concatenate a number with a 
    // blank string, you get a string    
    result = result + "";
    printWithType(result); //223 string
</script>

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