Javascript regex doesn't match

Question

I have been stucked with this problem for hours. I have a regex pattern and a matching string. Regarding to regex101.com, it is sure a matching string, but in my script, regarding to JSFiddle, it doesn't match.

RegExp: /\[img=?.*?http:\/\/lorempixel\.com\/640\/480.*?\/img\]/

String to match: [img=http://lorempixel.com/640/480]description[/img]

Script: JSFiddle

Can anyone find the problem here?

That's not how you build dynamic regex in JS, you need to use the RegExp constructor. — elclanrs
– elclanrs, Commented Jul 23, 2014 at 20:03
I have read somewhere (MDN or W3Schools), that strings convert to RegExp. Anyway, I am going to try your suggestion, thanks for the help. — helmet91
– helmet91, Commented Jul 23, 2014 at 20:05
Well, I tried it, aaaand, you are right! Thank you once again! @elclanrs — helmet91
– helmet91, Commented Jul 23, 2014 at 20:12
@helmet91 Just adding the RegExp constructor couldn't have fixed your problem. If it worked then you must have fixed the improper escaping in your string as well. — James Montagne
– James Montagne, Commented Jul 23, 2014 at 20:16
@JamesMontagne My original question aimed the RegExp constructor problem. However, as you said, I have another problem as well, but I don't want to ask too mutch. :D First, I am struggling with this new problem for another few hours. — helmet91
– helmet91, Commented Jul 23, 2014 at 20:44

Explosion Pills · Accepted Answer · 2014-07-23 20:42:51Z

2

You can't concatenate a regex using a regex literal, and you need a regex for the .match method.

var regex = new RegExp("\\[img=?.*?" + regexSafeUrl + ".*?\/img\\]");

http://jsfiddle.net/wue82/1/

EDIT: James Montague is correct that .match will implicitly use a RegExp. You don't need the / in the string that gets converted to RegExp though or these will be considered literal slashes. Your real problem was doing this as well as not properly escaping in the string.

http://jsfiddle.net/wue82/3/

edited Jul 23, 2014 at 20:42

answered Jul 23, 2014 at 20:05

Explosion Pills

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2 Comments

James Montagne Over a year ago

If a non-RegExp object obj is passed, it is implicitly converted to a RegExp by using new RegExp(obj). String.prototype.match

James Montagne Over a year ago

You missed one slash. The / before /img is still improperly escaped. Though it doesn't cause a problem since / doesn't need to be escaped at all.

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