This is a solution for validating an integer. Can someone please explain the logic of Karim's answer.
This works perfectly, but i am not able to understand how.
var intRegex = /^\d+$/;
if(intRegex.test(someNumber)) {
alert('I am an int');
...
}
The regex: /^\d+$/
^ // beginning of the string
\d // numeric char [0-9]
+ // 1 or more from the last
$ // ends of the string
when they are all combined:
From the beginning of the string to the end there are one or more numbers char[0-9] and number only.
Check out a Regular Expression reference: http://www.javascriptkit.com/javatutors/redev2.shtml
/^\d+$/
^ : Start of string
\d : A number [0-9]
+ : 1 or more of the previous
$ : End of string
A Nonnegative whole number is an "integer that is either 0 or positive."
Source: http://mathworld.wolfram.com/NonnegativeInteger.html
In other words, you are looking to validate a nonnegative integer.
The answers above are insufficient because they do not include integers such as -0 and -0000, which, technically, after parsing, become nonnegative integers. The other answers also do not validate integers with + in front.
You can use the following regex for validation:
/^(\+?\d+|-?0+)$/
Explanation:
^ # Beginning of String
( # Capturing Group
\+? # Optional '+' Sign
\d+ # One or More Digits (0 - 9)
| # OR
-? # Optional '-' Sign
0+ # One or More 0 Digits
) # End Capturing Group
$ # End of String
The following test cases return true: -0, -0000, 0, 00000, +0, +0000, 1, 12345, +1, +1234.
The following test cases return false: -12.3, 123.4, -1234, -1.
Note: This regex does not work for integer strings written in scientific notation.
This regex may be better /^[1-9]+\d*$/
^ // beginning of the string
[1-9] // numeric char [1-9]
+ // 1 or more occurrence of the prior
\d // numeric char [0-9]
* // 0 or more occurrences of the prior
$ // end of the string
Will also test against non-negative integers that are pre-padded with zeroes
000...(10,000 times)..000which is hardly a "number".