JS string into a number

Source: Internet
Author: User
Tags type casting

The three ways in which JS strings are converted into numbers are mainly

Conversion function, coercion type conversion, using JS variable weak type conversion.

1. Conversion function:

JS provides two conversion functions for parseint () and parsefloat (). The former converts the value into an integer, which converts the value into a floating-point number. Only these methods are called on the string type, and the two functions function correctly, and all other types return Nan (not a number).

Some examples are 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 that converts binary, octal, hexadecimal, or any other binary string into integers. The base is specified by the second parameter of the parseint () method, as in the following example:

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 a leading 0, it is best to use cardinality 10 so that the octal value is not unexpectedly obtained. For example:
parseint ("010"); Returns 8
parseint ("010", 8); Returns 8
parseint ("010", 10); Returns 10

The Parsefloat () method is similar to how the parseint () method is handled.
Another difference between using the Parsefloat () method is that the string must represent a floating-point number in decimal form, and parsefloat () has no base mode.

The following is an example of using the Parsefloat () method:
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

2. Forcing type conversions

You can also use the coercion type conversion (type casting) to handle the type of the converted value. A specific value can be accessed using a coercion type conversion, even if it is of a different type.
The 3 types of coercion conversions available in ECMAScript are as follows:
Boolean (value)-converts the given value to a Boolean type;
Number (value)-converts the given value to a digit (which can be an integer or a floating point);
String (value)-converts the given value to a string.
Using one of these three functions to convert the value, a new value is created that holds the value converted directly from the original value. This can cause unintended consequences.
The Boolean () function returns True when the value to be converted is a string of at least one character, a non-0 number, or an object (this is discussed in the next section). If the value is an empty string, the number 0, undefined, or null, it returns FALSE.

You can test a Boolean type cast with the following code snippet.

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

The coercion type conversion of number () is similar to the parseint () and parsefloat () methods, except that it transforms the entire value, not the partial value. Examples are as follows:

Usage results
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

The last method of forcing a type conversion is string (), which is the simplest example of the following:

var S1 = String (null); "NULL"
var onull = null;
var s2 = onull.tostring (); Won ' t work, causes an error

3. Using JS variable weak type conversion

A small example, a look, you will understand.
var str= ' 012.345 ';
var x = str-0;
x = x*1;

The above example uses the characteristics of the weak type JS, only the arithmetic operation, the implementation of the string to the number of the type conversion, but this method is not recommended

Transfer from http://blog.csdn.net/yf505261213/article/details/17374647

JS string into a number

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