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JavaScript/REGEX: Decimals Fail Number Validation without Leading 0

Posted on 2014-01-21
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Last Modified: 2014-01-21
This verifies an a string contains a number and only a number:
str.match(/^-?[0-9]\d*(.\d+)?$/g) 

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However these numbers fail:
.5
-.5

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They pass if there is a 0 before the decimal but I would like it to pass with or without the leading 0.
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Question by:hankknight
3 Comments
 
LVL 85

Assisted Solution

by:ozo
ozo earned 400 total points
ID: 39796795
You can omit the [0-9]
but then these would also verify as numbers:
-

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If you want at least one digit either before or after the decimal point, you might try something like
/^-?(\d+\.?|\.\d)\d*$/
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LVL 83

Assisted Solution

by:leakim971
leakim971 earned 400 total points
ID: 39796801
What not using isNaN ?
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/isNaN

isNaN("R")
true
isNaN("1")
false
isNaN("-1")
false
isNaN("-1f")
true
isNaN("1f")
true
0
 
LVL 43

Accepted Solution

by:
David S. earned 1200 total points
ID: 39796805
isNaN() would allow empty strings and strings only containing white-space characters though.

This should do it:
/^-?(\d*\.)?\d+$/g

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