truncating a string in javascript according to the REAL length of chars and tooltip the full-size string in the element

gistfile1.js

        //just to avoid 'string ...' with spaces
        //trim a string http://stackoverflow.com/a/498995
        String.prototype.trim=function(){return this.replace(/^\s\s*/, '').replace(/\s\s*$/, '');};

        //improvement of this: http://blog.mastykarz.nl/measuring-the-length-of-a-string-in-pixels-using-javascript/
	var visualLength = function(str){
		var ruler = document.createElement('span');
		ruler.style.visibility = 'hidden';
		ruler.style['white-space'] = 'nowrap';
		document.body.appendChild(ruler);
		ruler.innerHTML = str;
		var l =ruler.offsetWidth;
		document.body.removeChild(ruler);
		return l;		
	};

	var trunc = function(n, element){
		var str = element.innerHTML;
		if(visualLength(str)>n){
			do{
				str = str.substr(0,str.length-1).trim();
			}while(visualLength(str)>n);
			element.title = element.innerHTML;
			element.innerHTML=str + '…';
		}
	};

//usage (http://jsfiddle.net/B3QDd/)
trunc(100, $("foo"));