function _AJAXRequestStates(request, whenOk, whenFailed, atEnd) {

    if (request.readyState === 4) {
        if (request.status === 200) {
            if (whenOk !== undefined && whenOk !== null) {
                if (!checkIsAFunction(whenOk)) {
                    throw new Error("The parameter whenOk must be a function")
                }

                whenOk(request.responseText);
            }
        }

        else {
            if (whenFailed !== undefined && whenFailed !== null) {
                if (!checkIsAFunction(whenFailed)) {
                    throw new Error("The parameter whenFailed must be a function")
                }

                whenFailed(request.responseText);
            }
        }

        if (atEnd !== undefined && atEnd !== null) atEnd(request.responseText);
    }
}