A function which load the content of a json file.

loadJSON.js

// load JSON
function loadJSON(url, callback) {
    var xhr = new XMLHttpRequest();
    xhr.open('GET', url, true);
    xhr.onreadystatechange = function () {
        if (xhr.readyState === 4) {
            if (xhr.status === 200) {
                callback(JSON.parse(xhr.responseText));
            } else {
               //  callback([{}]);
            }
        }
    };
    xhr.send();
}