How to use variables inside Regular Expression in Javascript

Question

I want to build a RegEx in JavaScript that matches a word but not part of it. I think that something like \bword\b works well for this. My problem is that the word is not known in advance so I would like to assemble the regular expression using a variable holding the word to be matched something along the lines of:

r = "\b(" + word + ")\b";
reg = new RegExp(r, "g");
lexicon.replace(reg, "<span>$1</span>"

which I noticed, does not work. My idea is to replace specific words in a paragraph with a span tag. Can someone help me?

PS: I am using jQuery.

Answer 1

\ is an escape character in regular expressions and in strings.

Since you are assembling the regular expression from strings, you have to escape the \s in them.

r = "\\b(" + word + ")\\b";

should do the trick, although I haven't tested it.

You probably shouldn't use a global for r though (and probably not for reg either).

Answer 2

You're not escaping the backslash. So you should have:

r = "\\b(" + word + ")\\b"; //Note the double backslash
reg = new RegExp(r, "g");

Also, you should escape special characters in 'word', because you don't know if it can have regex special characters.

Hope this helps. Cheers