How can I add or update a query string parameter?

Question

With javascript how can I add a query string parameter to the url if not present or if it present, update the current value? I am using jquery for my client side development

Answer 1

Based on the answer @ellemayo gave, I came up with the following solution that allows for disabling of the hash tag if desired:

function updateQueryString(key, value, options) {
    if (!options) options = {};

    var url = options.url || location.href;
    var re = new RegExp("([?&])" + key + "=.*?(&|#|$)(.*)", "gi"), hash;

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

    if ((typeof options.hash === 'undefined' || options.hash) &&
        typeof hash[1] !== 'undefined' && hash[1] !== null)
        url += '#' + hash[1];
    return url;
}

Call it like this:

updateQueryString('foo', 'bar', {
    url: 'http://my.example.com#hash',
    hash: false
});

Results in:

http://my.example.com?foo=bar