Get & Set URL parameter in Javascript

get_set_url_param.js

function getURLParameter(name) {
    return decodeURIComponent(
        (RegExp('[?|&]'+name + '=' + '(.+?)(&|$)').exec(location.search)||[null,null])[1]
    );
}
function setURLParameter(name,value){
	var search;
	if(getURLParameter(name)){
		search =location.search.replace(new RegExp('([?|&]'+name + '=)' + '(.+?)(&|$)'),"$1"+encodeURIComponent(value)+"$3"); 
	}else if(location.search.length){
		search = location.search +'&'+name + '=' +encodeURIComponent(value);
	}else{
		search = '?'+name + '=' +encodeURIComponent(value);
	}
	History.pushState({state:History.getStateId()+1},document.title,search);
}

Uses https://github.com/balupton/history.js

Using regex for this is just wrong and will fail in some scenarios.

You'd better off using a tiny reusable module like:
https://github.com/sindresorhus/query-string