How to get JSON and put it into external variable?

Question

JavaScript

var JSONexternal = getJSON('/php/vesettingsforclient.php', function(response) {
    return JSON.parse(response);
});
console.log(JSONexternal); // undefined

function getJSON(url, callback) {
    var xhr = new getXmlHttpInstance();
    xhr.open("GET", url, true);
    xhr.send();
    xhr.onreadystatechange = function() {
        if (this.readyState == 4 && this.status == 200) {
            if (typeof callback === 'function') {
                callback.call(this, this.responseText); // как отсюда вытащить ответ во внешний скрипт?
            }
        }
    };
}

Answer 1

Because the getJSON function does not return anything, you get the value through a callback, in order for your code to work, you need to do this:

var JSONexternal = getJSON('/php/vesettingsforclient.php', function(response) {

   // response доступен только тут, эта функция вызывется асинхронно 
    console.log( JSON.parse(response));
});

function getJSON(url, callback) {
    var xhr = new getXmlHttpInstance();
    xhr.open("GET", url, true);
    xhr.send();
    xhr.onreadystatechange = function() {
        if (this.readyState == 4 && this.status == 200) {
            if (typeof callback === 'function') {
                callback.call(this, this.responseText); // как отсюда вытащить ответ во внешний скрипт?
            }
        }
    };
}

Answer 2

Is it possible that your callback expects one "response" and you give it two parameters? Try something like this:
I recommend logging to find out what is the reason. This is actually faster and more productive. There isn't much code. It is interesting what is returned in the response to the request and what is passed to your callback.
PS Do you have this.readyState, this.status and this.responseText working at all? Usually xhr.readyState, xhr.status and xhr.responseText.