JS 数值转换

2017-08-13 11:04:19 Albin Wong 521

## 数值转换
1. 转变成数字
    1. 转变成整型 parseInt()
    ```
    var str = '123456'; // 123456 number
    var str2 = 'iloveyou123456'; // NAN number
    var str3 = '1234iloveyou'; // 1234 number
    var res = parseInt(str);
    ```
    2. 转变成浮点型 parseFloat()
    ```
    var str4 = '3.1415926'; // 3.1415926 number
    var str5 = '2.33abcde'; // 2.33 number
    var str6 = 'ijklmn6.66'; // NAN number
    var res = parseFloat(str6);
    ```
    3. 转变成数字类型 Number()
    ```
    var a = true; // 1 number
    var b = false; // 0 number
    var c = null; // 0 number
    var d = '12345'; // 12345 number
    var e = '123asdfg'; // NAN number
    var f = 'asfc123'; // NAN number
    var h = new Array(); // 0 number
    var g = new Object(); // NAN number
    var j = function(){ // NAN number
        alert('222');
    }
    var i = ''; // 0 numebr
    var k = undefined; // NAN number
    var res = Number(k);
    alert(res);
    alert(typeof(res)); 
    ```
2. 转变成字符串
    ```
    var a = true; // 'true'
    var b = false; // 'false'
    var c = new Object(); // [object object]
    var d = new Array(); // ''
    var e = null; // 'null'
    var f = functon(){ // 代码体
        alert('222'); 
    }
    var g = undefined; // 'undefined'
    var h = 521; // '521'
    var i = 3.14; // '3.14'
    var j = 0x10; // '16'
    var i = 020; // '16'
    var res = String(i);
    ```
3. NAN
    1. NAN跟任何一个数字运算,结果都NAN
    2. 跟任何一个值比较,除了不等于,其他都是false 包括本身NAN
    检查NAN值
    ```
    var t = 1234;
    var res = isNAN(t);
    alert(res); // false
    ```
4.  转变成布尔类型(false,'',null,undefined,0,0.0)
```
var a = false; // false
var b = ''; // false
var c = '0'; // true
var d = undefined; // true
var e = null; // false
var f = 0; // false
var g = 0.0; // false
var g1 = NAN; //false
var res = Boolean(a);
console.log(res); // console(控制台) .(访问符) log(记录)
```
5. 自动类型转换
计算
```
var res = 123+123+'123'; // 246'123' 第三个+为字符串连接
var res = 123+'123'+123; // 123123123
var res = 999 - '123'; // 876
var res = 987 - '123abc'; // NAN
```
// 判断if
```
var test = '100';
var test = ''; // x
var test = 10>20; // x
if(test){
    alert(123);
}
```

(3) Comments

John Doe- Reply

February 26, 2013 at 1:18 pm
- saqib sarwar- Reply
  
  February 26, 2013 at 1:20 pm
  
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John Doe- Reply

February 26, 2013 at 1:27 pm

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JS 数值转换

(3) Comments

John Doe- Reply

saqib sarwar- Reply

John Doe- Reply

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