Shorten a long string of HTML to a predetermined length and append with '...'

string.shorten.js

String.prototype.shorten = function( length ) {
	//shorten a string while minding the possible HTML markup within
	var original = this.toString()
	,	length = length || 500
	,	tagRE = /<\/?\w+(\s+\w+="?[^>]*"?)*\s*>/g
	,	openTagRE = /<[^>\/]*([^\/]*>)/g
	,	closeTagRE = /<[\/]([^\/]*>)/g
	,	pipeRE = /\|/
	,	tag = ''
	,	tags = original.match( tagRE )
	,	tagDepth = 0
	,	htmlTagless = original.replace( tagRE, '|' ).replace( /\s+/g, ' ' ).replace( /(^\s|\s$)/g, '' ) //replace HTML tags with pipe, then consecutive spaces with single space, then leading and trailing spaces
	,	substrings = htmlTagless.match( new RegExp( '(.{' + length + '})' ) )
	;

	var truncated = ( substrings && substrings[ 1 ] ) ? substrings[ 1 ].replace( /\w+$/, '...' ) : original;
	
	while( truncated.match( /\|/ ) && tags.length ) { //convert any pipes back to tags
	    tag = tags.shift();
	    if ( tag.match( openTagRE ) ) { //an open tag increases the tag depth
	        tagDepth++;     
	    } else if ( tag.match( closeTagRE ) ) { //a close tag decreases the tag depth
	        tagDepth--;
	    }
	    truncated = truncated.replace( pipeRE, tag );
	}
	while ( tagDepth && tags.length ) {
	    tag = tags.shift();
	    if ( tag.match( closeTagRE ) ) {
	        truncated += tag;
	        tagDepth--;
	    }
	}
	return truncated;
}