util for text search/replace for DOM output

fragger.js

var fragger = {
	root : null,
	cur_root : null, //ungh, but I can't find a better place...
	last_index : null,

	new : function () {
		return Object.create( this );
	},

	init : function ( text ) {
		this.root = document.createDocumentFragment();
		this.root.appendChild( document.createTextNode(text) );
	},

	replace : function ( re, fun ) {
		this.last_index = 0;
		var list = this.getTextNodes(),
			bound = this.actual_replace.bind( this, fun ),
			cur;

		while ( cur = list.pop() ) {
			this.cur_root = document.createDocumentFragment();

			cur.data.replace( re, bound );
			this.append_text( cur.data, this.last_index );

			this.root.replaceChild( this.cur_root, cur );
		}

		return this.root;
	},

	/*
	For getting this far through the code, here is some pie:

	         (
	          )
	     __..---..__
	 ,-='  /  |  \  `=-.
	:--..___________..--;
	 \.,_____________,./
	*/

	actual_replace : function ( cb, match ) {
		var args   = [].slice.call( arguments ),
			str    = args[ args.length - 1 ],
			offset = args[ args.length - 2 ];

		this.append_text( str, this.last_index, offset );

		var node = cb.apply( null, args.slice(1) );
		if ( node && node.nodeType ) {
			this.cur_root.appendChild( node );
			this.last_index = offset + match.length;
		}
	},

	append_text : function ( str, begin, end ) {
		if ( begin === end ) {
			return;
		}
		var node = document.createTextNode();
		node.data = str.slice( begin, end );

		this.cur_root.appendChild( node );
	},

	getTextNodes : function () {
		return [].filter.call( this.root.childNodes, text_node_check );

		function text_node_check ( node ) {
			return node && node.nodeType === 3;
		}
	}
};

usage.js

var frag = fragger.new();
frag.init( 'foobar' );
frag.replace( /foo/, replacer );
document.body.appendChild( frag.root );
//instead of directly accessing frag.root, you can store the result of frag.replace

//input: the capturing groups
function replacer ( $0 ) {
    var ret = document.createElement( 'div' );
    ret.textContent = 'lulz ' + $0;
    //output: node to replace caught text with
    // if you want just text, return a text node
    return ret;
}

//you can see it in action either here:
// http://zirak.github.com/SO-ChatBot/
//as the mini-md formatter, or in this demo:
// http://tinkerbin.com/E5ZL7RV7