Regex match for specific number before but not after in javascript

Question

I just suck at regex. I've been reading at http://www.regular-expressions.info/tutorial.html but I can't figure out how to write this.

I have a string that contains 2 numbers (days of the month with leading 0s). I'm trying to remove the leading 0s from the string but not remove the 0 in "10" or "20".

example strings that could be here: "01","02","03","10","11","12","20","31"

since the string is always a day of the month, it will always be 2 characters in length and always between 01 and 31.

currently I'm using this (which is obviously wrong):

string.replace(/0/,'');

What I'm trying to end up with is this: "1" instead of "01", "2" instead of "02", "10" without losing the "0".

Hopefully this is clear enough.

How do I do this correctly?

Can you post an example string? Is it always a known format, or does it vary? — Chris Sobolewski
– Chris Sobolewski, Commented Feb 7, 2013 at 3:20
Can you show the actual text we're matching against? Not sure if it is 20130206 or 02-06-2013 or 02//06/2013 or... — Devin Ceartas
– Devin Ceartas, Commented Feb 7, 2013 at 3:21

Qtax · Accepted Answer · 2013-02-07 04:06:09Z

1

If the string only contains the number you could just convert it to an integer, eg:

var num = +str;

If you want to replace parts of a larger string, you can use \b:

str.replace(/\b0+\B/g, '');

Example:

"i have 000100 and 0020!".replace(/\b0+\B/g, '')

Returns:

"i have 100 and 20!"

edited Feb 7, 2013 at 4:06

answered Feb 7, 2013 at 3:20

Qtax

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7 Comments

codescribblr Over a year ago

This did it. str.replace(/\b0\B/, ''); Thank you!

codescribblr Over a year ago

Would you mind explaining what \b does? I realize that \B would be the negation of it, but I don't know what \b stands for.

Devin Ceartas Over a year ago

"b" is for "boundary" - the edge of the character class. If you think this is the correct answer, you should accept it so others will know when they are looking for the answer. They might miss the comments.

Qtax Over a year ago

@Jonathan, as Devin points out, \b is for (word) boundary. It is a zero width assertion (like a lookahead), and if JavaScript had lookbehinds could be written as (?:(?<=\w)(?!\w)|(?<!\w)(?=\w)).

nhahtdh Over a year ago

How does var num = 0 + str; has anything to do with the solution?

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