Three ways to convert js strings into numbers

Whenjsreads text boxes or other form data, the value obtained is of string type,For example, two text boxesaandb,If you get## The#valueof #ais11, and thevalue## of b#The value is9,thena.valueshould be less thanb.value,Because they are all in the form of strings.There are three main methods: conversion function, forced type conversion, and using

js

variable weakness Type conversion.

Conversion function

js

provides

parseInt()andparseFloat()Two conversion functions. The former converts the value into an integer, and the latter converts the value into a floating point number. Only by calling these methods on theStringtype can these two functions run correctly; for other types, they returnNaN(Not a Number).Some examples are as follows:

The code is as follows

:

parseInt("1234blue"); //returns 1234 parseInt("0xA"); //returns 10 parseInt("22.5"); //returns 22 parseInt("blue"); //returns NaN

The parseInt()

method also has a base mode, which can convert binary, octal, hexadecimal or any other base string into an integer. The base is specified by the second parameter of the

parseInt()method. The example is as follows:The code is as follows

:

parseInt("AF", 16); //returns 175 parseInt("10", 2); //returns 2 parseInt("10", 8); //returns 8 parseInt("10", 10); //returns 10

## If the decimal number contains the leading
0

, then it is better to use the base10, so that you don't accidentally get an octal value. For example:The code is as follows:

parseInt("010"); //returns 8 parseInt("010", 8); //returns 8 parseInt("010", 10); //returns 10

## The parseFloat()method is the same as

parseInt()

The method is handled similarly.Another difference in using theparseFloat()

method is that the string must represent a floating point number in decimal form,

parseFloat()There is no base pattern.The following is an example of using theparseFloat()

method:

The code is as follows:

parseFloat("1234blue"); //returns 1234.0 parseFloat("0xA"); //returns NaN parseFloat("22.5"); //returns 22.5 parseFloat("22.34.5"); //returns 22.34 parseFloat("0908"); //returns 908 parseFloat("blue"); //returns NaN

## Forced type conversion

You can also use forced type conversion (

type casting) Handle the type of converted value. Use a cast to access a specific value, even if it is of another type. The

ECMAScript#3

forced type conversions available are as follows:Boolean(value)——Convert the given value into theBoolean

type;Number(value)——Convert the given value into Number (can be an integer or floating point number);

String(value)

- Convert the given value to a string.

用这三个函数之一转换值，将创建一个新值，存放由原始值直接转换成的值。这会造成意想不到的后果。

当要转换的值是至少有一个字符的字符串、非0数字或对象（下一节将讨论这一点）时，Boolean()函数将返回true。如果该值是空字符串、数字0、undefined或null，它将返回false。

可以用下面的代码段测试Boolean型的强制类型转换。

代码如下:

Boolean(""); //false – empty string Boolean("hi"); //true – non-empty string Boolean(100); //true – non-zero number Boolean(null); //false - null Boolean(0); //false - zero Boolean(new Object()); //true – object

Number()的强制类型转换与parseInt()和parseFloat()方法的处理方式相似，只是它转换的是整个值，而不是部分值。示例如下：

代码如下:

Number(false) 0 Number(true) 1 Number(undefined) NaN Number(null) 0 Number( "5.5 ") 5.5 Number( "56 ") 56 Number( "5.6.7 ") NaN Number(new Object()) NaN Number(100) 100

最后一种强制类型转换方法String()是最简单的，示例如下：

代码如下:

var s1 = String(null); //"null" var oNull = null; var s2 = oNull.toString(); //won't work, causes an error

利用js变量弱类型转换

代码如下:

上例利用了js的弱类型的特点，只进行了算术运算，实现了字符串到数字的类型转换，不过这个方法还是不推荐的。

美文美图

以上就是JavaScript进阶(四)js字符串转换成数字的三种方法的内容，更多相关内容请关注PHP中文网（m.sbmmt.com）！