function nl2br(){

	var text = escape(this);
	var re_nlchar = null;

	if(text.indexOf('%0D%0A') > -1)
	{
		re_nlchar = /%0D%0A/g ;
	}
	else if(text.indexOf('%0A') > -1)
	{
		re_nlchar = /%0A/g ;
	}
	else if(text.indexOf('%0D') > -1)
	{
		re_nlchar = /%0D/g ;
	}
	
	text = (re_nlchar != null) ? unescape(text.replace(re_nlchar,'<br />')) : unescape(text);
	return text
}

String.prototype.nl2br = nl2br;

This will need to be either embeded or included and you can then just use this as such

myNewString = myStringVariable.nl2br();

Replace Newlines with BR, String Prototype

replace

JavaScript