replace with regexp return undefined

Question

I'm not so bad in regular expression but there I have a tiny problem, maybe one of you can answer this simple question.

I do this:

var myString = "10px";
var myRegexp = new RegExp("(\\d*\\.?\\d*){1}(em|ex|grad|ch|deg|ms|rad|rem|s|turn|vh|vw|vmin|vmax|px|cm|in|pt|pc|%)?", "gi");

myString.replace(myRegexp, function( match, number, type ){
    console.log(match, number, type);
});

The replace console log two time, the first is : "10px", "10", "px" and I don't know why there is a second time, it return me that: ,,undefined (the two first value are not null or empty string, they return just nothing, absolutely empty).

My question, why the replace try a seconde replacing on nothing ? And how avoid it ?

Minor thing: {1} is completely pointless

freefaller
– freefaller

2014-03-27 10:25:23 +00:00
Commented Mar 27, 2014 at 10:25 — freefaller
– freefaller, Commented Mar 27, 2014 at 10:25

anubhava · Accepted Answer · 2014-03-27 10:36:29Z

3

Instead of:

 (\\d*\\.?\\d*){1}

Use start anchor:

^(\\d*\\.?\\d*)

As your regex has everything optional and matches empty string also.

edited Mar 27, 2014 at 10:36

answered Mar 27, 2014 at 10:27

anubhava

790k67 gold badges603 silver badges671 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Jordan Over a year ago

Yes this solve the problem but if value is .5, the regexp dont match.

Jordan Over a year ago

I find another solution, but the start anchor look better, it is (\\d*\\.\\d*|\\.)...

Ron Rosenfeld Over a year ago

@anubhava I believe the OP wants to always match a number. Your proposal will match an empty line

Jordan Over a year ago

Nothing ! Your answer is good, the problem is my example, I said "10px". It is only cause of the start anchor cant find 10px in "translateX(10px)", I did not think well before asking the question, I can't replace nothing by something, so the answer of Ron is better for avoiding any other problem. The solution is to do not search nothing. :)

Ron Rosenfeld · Accepted Answer · 2014-03-27 10:44:22Z

1

I think it is because your expression has everything optional, so you are also matching a zero-length string (an issue with javascript). If I understand what you want to do, I don't think the number has to be optional, so you could try:

(\d*\.?\d+)(em|ex|grad|ch|deg|ms|rad|rem|s|turn|vh|vw|vmin|vmax|px|cm|in|pt|pc|%)?

answered Mar 27, 2014 at 10:44

Ron Rosenfeld

62k7 gold badges35 silver badges71 bronze badges

Collectives™ on Stack Overflow

replace with regexp return undefined

2 Answers 2

4 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related