Getting and Setting URL Parameters with JavaScript

Although there’s probably plenty of good plugins to do this my code for getting and setting URL parameters is below. These take the URL to parse as an argument as I wanted to be able to update parameters in linked URLs as well as the current URL which would be provided by window.location.

function getUrlParameter(url, parameter){
	parameter = parameter.replace(/[\[]/, '\\[').replace(/[\]]/, '\\]');
	var regex = new RegExp('[\\?|&]' + parameter.toLowerCase() + '=([^&#]*)');
	var results = regex.exec('?' + url.toLowerCase().split('?')[1]);
	return results === null ? '' : decodeURIComponent(results[1].replace(/\+/g,''));
}

Below is an updated version of the setUrlParameter function which better handles null and URI encoded parameters courtesy of Paul’s comment 🙂

function setUrlParameter(url, key, value) {
	var key = encodeURIComponent(key),
		value = encodeURIComponent(value);

	var baseUrl = url.split('?')[0],
		newParam = key + '=' + value,
		params = '?' + newParam;

	if (url.split('?')[1] === undefined){ // if there are no query strings, make urlQueryString empty
		urlQueryString = '';
	} else {
		urlQueryString = '?' + url.split('?')[1];
	}

	// If the "search" string exists, then build params from it
	if (urlQueryString) {
		var updateRegex = new RegExp('([\?&])' + key + '=[^&]*');
		var removeRegex = new RegExp('([\?&])' + key + '=[^&;]+[&;]?');

		if (value === undefined || value === null || value === '') { // Remove param if value is empty
			params = urlQueryString.replace(removeRegex, "$1");
			params = params.replace(/[&;]$/, "");
	
		} else if (urlQueryString.match(updateRegex) !== null) { // If param exists already, update it
			params = urlQueryString.replace(updateRegex, "$1" + newParam);
	
		} else if (urlQueryString == '') { // If there are no query strings
			params = '?' + newParam;
		} else { // Otherwise, add it to end of query string
			params = urlQueryString + '&' + newParam;
		}
	}

	// no parameter was set so we don't need the question mark
	params = params === '?' ? '' : params;

	return baseUrl + params;
}