How to add a javascript regular expression escape character dynamically

Question

I have a line of code as follows

if($('#eqInputBox').val().search( $(this).html() ) == -1)

Which is supposed to check to see the html is already in the eqInputBox or not - problem is, sometimes the character in $(this).html() can be a '+' or a '*'. Any other character (in the set of possible characters for the app) works, but when these characters show up, the regular expression doesn't return any value - I think this might be because I can't slip a \ character in to escape these characters.

Anyone have any ideas on how, when the (this) html character is + or *, I can still make it check normally?

EDIT:

$(this).html()

is a user generated div, so I cannot simply put the escape character in manually. How would I go about dynamically adding it when it is necessary?

Dave, that fixed it! Just replacing it with \\$1 that's exactly what I was looking for - thanks a lot! (Only problem is I can't mark this question as answered because you didn't post the response as an answer :-P) — Anthony
– Anthony, Commented Nov 22, 2011 at 7:25
Looks like $('#eqInputBox').val().indexOf($(this).html()) is enough. — Leonid
– Leonid, Commented Nov 22, 2011 at 11:07

Toto · Accepted Answer · 2011-11-22 09:40:44Z

3

You have to simulate quotemeta, have a look at Escaping regular expression

RegExp.escape = function(text) {
    return text.replace(/[-[\]{}()*+?.,\\^$|#\s]/g, "\\$&");
}

answered Nov 22, 2011 at 9:40

Toto

91.7k63 gold badges97 silver badges135 bronze badges

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

1 Comment

Anthony Over a year ago

This is a very useful function to automatically escape characters - helps a lot, thanks!

Saeed Neamati · Accepted Answer · 2011-11-22 07:19:43Z

2

The value of $(this).html() should be a valid Regular Expression pattern. In other words, instead of having d*, you should write \d* in it.

Thus you should escape characters statically, while creating the value of $(this).html().

Update: Since the value of $(this).html() is generated by user, you can create a helper function to detect special regular expression characters and escape it in that function.

function escapeCharacters(patter){
    // Here escape special characters. Eg. d* to \d*. However, it's difficulat
}

then use it this way:

if($('#eqInputBox').val().search( escapeCharacters($(this).html()) ) == -1)

edited Nov 22, 2011 at 7:19

answered Nov 22, 2011 at 6:18

Saeed Neamati

35.9k42 gold badges140 silver badges192 bronze badges

1 Comment

Anthony Over a year ago

You are right, the only problem is the $(this).html() is a user generated string, so it won't have the escape character when they enter it. Do you know any way to dynamically add this character to the RegExp at runtime?

eric.itzhak · Accepted Answer · 2021-08-03 08:54:27Z

1

MDN Docs suggest a slightly different regex than Toto answered:

function escapeRegExp(string) {
  return string.replace(/[.*+?^${}()|[\]\\]/g, '\\$&'); // $& means the whole matched string
}

answered Aug 3, 2021 at 8:54

eric.itzhak

16.2k28 gold badges96 silver badges147 bronze badges

Collectives™ on Stack Overflow

How to add a javascript regular expression escape character dynamically

3 Answers 3

1 Comment

1 Comment

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related