Adding a parameter to the URL with JavaScript

Question

In a web application that makes use of AJAX calls, I need to submit a request but add a parameter to the end of the URL, for example:

Original URL:

Answer 1

Try
The regular expressions, so slow, thus:

var SetParamUrl = function(_k, _v) {// replace and add new parameters

    let arrParams = window.location.search !== '' ? decodeURIComponent(window.location.search.substr(1)).split('&').map(_v => _v.split('=')) : Array();
    let index = arrParams.findIndex((_v) => _v[0] === _k); 
    index = index !== -1 ? index : arrParams.length;
    _v === null ? arrParams = arrParams.filter((_v, _i) => _i != index) : arrParams[index] = [_k, _v];
    let _search = encodeURIComponent(arrParams.map(_v => _v.join('=')).join('&'));

    let newurl = window.location.protocol + "//" + window.location.host + window.location.pathname + (arrParams.length > 0 ? '?' +  _search : ''); 

    // window.location = newurl; //reload 

    if (history.pushState) { // without reload  
        window.history.pushState({path:newurl}, null, newurl);
    }

};

var GetParamUrl = function(_k) {// get parameter by key

    let sPageURL = decodeURIComponent(window.location.search.substr(1)),
        sURLVariables = sPageURL.split('&').map(_v => _v.split('='));
    let _result = sURLVariables.find(_v => _v[0] === _k);
    return _result[1];

};

Example:

        // https://some.com/some_path
        GetParamUrl('cat');//undefined
        SetParamUrl('cat', "strData");// https://some.com/some_path?cat=strData
        GetParamUrl('cat');//strData
        SetParamUrl('sotr', "strDataSort");// https://some.com/some_path?cat=strData&sotr=strDataSort
        GetParamUrl('sotr');//strDataSort
        SetParamUrl('cat', "strDataTwo");// https://some.com/some_path?cat=strDataTwo&sotr=strDataSort
        GetParamUrl('cat');//strDataTwo
        //remove param
        SetParamUrl('cat', null);// https://some.com/some_path?sotr=strDataSort