A handy Javascript function to add/update/remove a GET parameter from a URI.

setURIParameter.js

// add or update a GET variable in a URL
function setURIParameter(uri, key, value) {
	if (uri.indexOf("&") >= 0) {
		console.log("Warning: setURIParameter expects an unencoded URI. This looks like an encoded URI (found &).");
	}

	// just append the key-value pair to the end of the URI if this parameter isn't present
	if (uri.indexOf("?" + key) === -1 && uri.indexOf("&" + key) === -1) {
		// support key deletion via a recursive call (so don't add it back)
		if (value.length === 0) {
			return uri;
		}

		if (uri.indexOf("?") >= 0) {
			return uri + "&" + key + "=" + value;
		} else {
			return uri + "?" + key + "=" + value;
		}
	} else {
		// remove the parameter then make a recursive call (which will append the value to the end)
		var stripped_uri = uri.replace(new RegExp(key + "=[a-zA-Z0-9_-]*&?", "g"), "");

		// don't leave garbage ? or & at the end
		if (stripped_uri.substr(-1) == "?" || stripped_uri.substr(-1) == "&") {
			stripped_uri = stripped_uri.substr(0, stripped_uri.length - 1);
		}

		return setURIParameter(stripped_uri, key, value);
	}
}