Javacript: Set or Update a URL/QueryString Parameter, and update URL using HTML history.replaceState()

update-url-query-string-history.js

// Explicitly save/update a url parameter using HTML5's replaceState().
function updateQueryStringParam(key, value) {
    const baseUrl = [location.protocol, '//', location.host, location.pathname].join('');
    const urlQueryString = document.location.search;
    let newParam = key + '=' + value;
    let params = '?' + newParam;

    // If the "search" string exists, then build params from it
    if (urlQueryString) {
        const keyRegex = new RegExp('([\?&])' + key + '[^&]*');
        // If param exists already, update it
        if (urlQueryString.match(keyRegex) !== null) {
            params = urlQueryString.replace(keyRegex, "$1" + newParam);
        } else { // Otherwise, add it to end of query string
            params = urlQueryString + '&' + newParam;
        }
    }

    window.history.replaceState({}, "", baseUrl + params);
}