Change a query parameter in the current URL.

changeUrlParam.js

function changeUrlParam(paramName, newValue) {
	var search = location.search.replace(new RegExp('[?&]' + paramName + '=[^&]+'), ''),
		url = location.pathname + search;
	
	if (newValue !== null) {
		url += (search ? '&' : '?') +
			paramName + '=' + newValue;
	}
	
	location = url;
}

gistfile1.md

For URL /foo/bar?param=5 the code changeUrlParam('param', 6) will redirect to /foo/bar?param=6
For URL /foo/bar?param=5 the code changeUrlParam('param', null) will redirect to /foo/bar