RegEx match only words with no specific words before and after

Question

I'm currently writing a function in Javascript which tags specific words.

I have a Box called <code> ... </code> in which i will be writing JS code. I am to lazy to set all tags for syntax highlighting by myself, so i want to have a function to do that for me.

Example: <obj>this</obj>.functionName(); <- obj tag will hightlight "this" in a specific color.

But if "this" wasn't tagged and occurs like that:

<tab></tab> this.functionName() ;

I want to tag it, but not the already tagged "this" .

Here is my JS code:

function hightLight(text, tag, html) {
   var taggedText = ("<" + tag + ">" + text + "</" + tag + ">");
   var oldHTML = "";
   do {
       oldHTML = html;
       html = html.replace(text, taggedText);
   } while(html.localeCompare(oldHTML) != 0);//stop if nothing changed
   return html;
}

Answer 1

Use this regex:

/this(?!<\/tab>)/

It uses a negative lookahead so it only matches this when it is not followed by </tab> . You could use it like this:

var regex = new RegExp(text + "(?!</" + tag + ">)");

and

html = html.replace(regex, taggedText);