Javascript Regexp - Match string pattern except if string is inside specified tag

Question

Hello

I am trying to replace all occurences of ???some.text.and.dots??? in a html page to add a link on it. I've built this regexp that does it :

\?\?\?([a-z0-9.]*)\?\?\?

However, I would like to exclude any result that is inside a link : "<a ...> ... MY PATTERN ... </a>", and I am a little stuck as to how to do that, all my attempts have failed for now.

Answer 1

JavaScript doesn't inherently support look-behind. In order to do this, you'd need to run .match() and then for each of your matches, you'd need to do matches on your tags (such as /<a\s+.*?>/ being immediately before your match and then </a> after your match).

Good luck!!

Answer 2

It's not really clear what kind of "HTML" you are working on. If it is HTML code, something from an Ajax request maybe, then you can use a regular expression; matching both a link or the pattern, and then work out what to do in a callback:

var html = document.body.innerHTML;
html = html.replace(/(<a\s.*?>.*?<\/a>)|(\?\?\?([a-z0-9.]*)\?\?\?)/g, 
    function ( a, b, c, d ) {
       return ( a[0] == '<' ) ? a : '<a href="#">' + d + '</a>'; 
    });
context.innerHTML = html;

Conveniently, replace() can take a callback function as a replacement generator rather than a simple string.

If you are working on a live DOM tree, however, you might want to respect events on nodes and not simply reset the innerHTML. You'll need a bit more primitive approach for that:

// returns all childnodes of type text that do not have A as parent
function walker ( node ) {
  var nodes = [];
  for (var c, i = 0; c = node.childNodes[i]; i++) {
    if ( c.nodeType === 1 && c.tagName !== 'A' ) {
      nodes = nodes.concat( arguments.callee( c ) );
    }
    else if ( c.nodeType === 3 ) { 
      nodes.push( c );
    }
  }
  return nodes;
}

var textNodes = walker( document.body );
for (var i = 0; i < textNodes.length; i++) {
  // create an array of strings separating the pattern
  var m = textNodes[i].nodeValue.split( /(\?\?\?([a-z0-9.]*)\?\?\?)/ );
  if ( m.length > 1 ) {
    for (var j=0; j<m.length; j++) {
      var t, parent = textNodes[i].parentNode;
      // create a link for any occurence of the pattern
      if ( /^\?\?\?([a-z0-9.]*)\?\?\?$/.test( m[j] ) ) {
        var a = document.createElement( 'a' );
        a.href = "#";
        a.innerHTML = RegExp.$1;  // m[j] if you don't want to crop the ???'s
        parent.insertBefore( a, textNodes[i] );
        t = document.createTextNode( ' ' ); // whitespace padding
      }
      else {
        t = document.createTextNode( m[j] );
      }
      parent.insertBefore( t, textNodes[i] );
    }
    // remove original text node
    parent.removeChild( textNodes[i] );
  }
}

This method only touches textnodes, and then only those that match the pattern.