JavaScript字符串和数字转换

Question

如何在JavaScript中执行以下操作？

1. 将"1","2","3"连接成"123"

2. 将"123"转换为123

3. 添加123 + 100 = 223

4. 隐藏223成"223"

Answer 1

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:

<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>

Answer 2

步骤(1)将"1","2","3"连接成"123"

 "1" + "2" + "3"

要么

 ["1", "2", "3"].join("")

该加入方法串接数组的项转换成字符串,将项目间的指定的分隔符.在这种情况下,"分隔符"是一个空字符串("").

步骤(2)将"123"转换为123

 parseInt("123")

在ECMAScript 5之前,有必要传递基数为10的基数:parseInt("123", 10)

步骤(3)添加123 + 100 = 223

 123 + 100

步骤(4)将223隐藏为"223"

 (223).toString() 

把它放在一起Togther

 (parseInt("1" + "2" + "3") + 100).toString()

要么

 (parseInt(["1", "2", "3"].join("")) + 100).toString()

Answer 3

r = ("1"+"2"+"3")           // step1 | build string ==> "123"
r = +r                      // step2 | to number    ==> 123
r = r+100                   // step3 | +100         ==> 223
r = ""+r                    // step4 | to string    ==> "223"

//in one line
r = ""+(+("1"+"2"+"3")+100);

Answer 4

由于JavaScript的打字系统,这些问题一直存在.人们认为他们在得到一个数字的字符串时会得到一个数字.

以下是您可能会看到的一些利用JavaScript处理字符串和数字的方式.就个人而言,我希望JavaScript使用除+之外的一些符号来进行字符串连接.

步骤(1)将"1","2","3"连接成"123"

result = "1" + "2" + "3";

步骤(2)将"123"转换为123

result = +"123";

步骤(3)添加123 + 100 = 223

result = 123 + 100;

步骤(4)将223转换为"223"

result = "" + 223;

如果你知道为什么这些工作,你就不太可能遇到JavaScript表达式的麻烦.

Answer 5

你可以这样做:

// step 1 
var one = "1" + "2" + "3"; // string value "123"

// step 2
var two = parseInt(one); // integer value 123

// step 3
var three = 123 + 100; // integer value 223

// step 4
var four = three.toString(); // string value "223"

Answer 6

要将字符串转换为数字,请减去0.要将数字转换为字符串,请添加""(空字符串).

5 + 1会给你6

(5 +"")+ 1会给你"51"

("5" - 0)+ 1会给你6

Answer 7

parseInt像scanf一样错误:

__PRE__