JSFiddle - React, Tailwind, and code Playground

JavaScript

window.getParameter = function(paramName, url) {
    if (! paramName) {
        return null;
    }
    if (! url) {
        url = window.location.href;
    }
    if (url.indexOf('?') == -1) {
        return null;
    }
    url = url.substring(url.indexOf('?') + 1);
    var params = url.split('&');
    for (var index = 0; index < params.length; index++) {
        var nameValue = params[index].split('=');
        if (nameValue.length == 2 && nameValue[0] == paramName) {
            return nameValue[1];
        }
    }
    
    return null;
};
    
alert('client=' + getParameter("client", "http://someurl.com?a=5&client=bcdefg&d=7"));