Edit in JSFiddle

var testUrl1 = 'https://www.youtube.com/watch?v=qyCtwmlz1Dw';
var testUrl2 = 'http://www.amazon.it/s/ref=nb_sb_noss_2?&url=search-alias%3Daps&field-keywords=arduino';

//parameter ok but without value
var testUrl3 = 'https://www.youtube.com/watch?v=';

//multiple quesiton ? chars
var testUrl4 = 'http://www.amazon.it/s/ref=nb_sb_noss_2?&url=search-alias?Daps&field-keywords=arduino';

//search for parameter 'v' and 'field-keywords' in url
$('#result').append(getUrlParameterValue(testUrl1, 'v') + '<br/>');
$('#result').append(getUrlParameterValue(testUrl2, 'field-keywords') + '<br/>');

//search somethings not exist
$('#result').append(getUrlParameterValue(testUrl1, 'fake-parameter') + '<br/>');
$('#result').append(getUrlParameterValue(testUrl1, 'other-fake') + '<br/>');

$('#result').append(getUrlParameterValue(testUrl3, 'v') + '<br/>');

$('#result').append(getUrlParameterValue(testUrl4, 'url') + '<br/>');

function getUrlParameterValue(url, parameter) {
    var questionSplit = url.split('?');
    //prevent multiple split if more then one quesiton (?) char
    questionSplit.shift();
    var onlyParameters = questionSplit.join('?');
    var splittedParameters = onlyParameters.split('&');
    var found = false;
    var value = null;
    for (var c = 0; c < splittedParameters.length; c++) {
        var parts = splittedParameters[c].split('=');
        if (parts[0] == parameter) {
            value = parts[1];
            if ($.trim(value) == '') {
                found = false;
            } else {
                found = true;
            }
        }
        if (found) {
            return value;
        }
    }
    if (!found) {
        return false;
    }
}

<div id="result"></div>