js query param replacer

function addOrReplaceQueryParam(url,param,value) {
    var re = new RegExp("([?|&])" + param + "=.*?(&|$)","i");
    var paramCount = url.split("?").length - 1;
    var separator = url.indexOf('?') !== -1 ? '&' : '?',

    if (url.match(re)) 
    {
        return url.replace(re, '$1' + param + "=" + value + '$2');
    }
    else 
    {   
        return url + separator + param + "=" + value;
    }
}

v2

pdateQueryParam = function(key, value, url) {
	    if (!url) url = window.location.href;
	    var re = new RegExp("([?|&])" + key + "=.*?(&|#|$)(.*)", "gi");
	
	    if (re.test(url)) {
	        if (typeof value !== 'undefined' && value !== null)
	            return url.replace(re, '$1' + key + "=" + value + '$2$3');
	        else {
	            return url.replace(re, '$1$3').replace(/(&|\?)$/, '');
	        }
	    }
	    else {
	        if (typeof value !== 'undefined' && value !== null) {
	            var separator = url.indexOf('?') !== -1 ? '&' : '?',
	                hash = url.split('#');
	            url = hash[0] + separator + key + '=' + value;
	            if (hash[1]) url += '#' + hash[1];
	            return url;
	        }
	        else
	            return url;
	    }
	}