ES6承诺和阶级冲突

我很困惑为什么有时当我使用一个类的实例和一个承诺的组合我得到两种错误.如果我使用带有两个或三个链式承诺的Promise.all(),我有时只会在回调中得到一个未定义变量的错误.当我有一个包含多个属性和方法的复杂类时,我有一个未定义的类的实例与我的.then() 如果我的类很简单,我只使用一个或两个链式的promises我没有错误.有没有人知道为什么会这样？以下是我的目标代码结构示例:

(代码在最新的Firefox Nightly中正确执行,但在Chrome 47中没有执行)

'use strict';

class Controller {
	constructor() {
		this.data = 'data';
		this.moredata = 'data';
		this.evenmore = ['a', 'b', 'c'];
		this.dataobj = {"a" : "1", "b" : "2", "c" : "3"};
	}
}

//BLOCKED CODE
{
	let cc = new Controller();
	let loadeddata = null;
	
	let xhr = $.getJSON('chapters.json', {}, (response) => {
		loadeddata = response; //SOMETIMES IF CLASS IS COMPLEX IS NOT DEFINED (SOMETIMES IT IS)
	}).fail(() => {
		console.log('Failed to load JSON data!');
	});
	
	let xhr2 = $.getJSON('chapters.json', {}, (response) => {
		loadeddata = response;
	}).fail(() => {
		console.log('Failed to load JSON data!');
	});
	
	let xhr3 = $.getJSON('chapters.json', {}, (response) => {
		loadeddata = response;
	}).fail(() => {
		console.log('Failed to load JSON data!');
	});
	
	let xhr4 = $.getJSON('chapters.json', {}, (response) => {
		loadeddata = response;
	}).fail(() => {
		console.log('Failed to load JSON data!');
	});
	
	
	//SOMETIMES WITH COMPLICATED CLASS WITH ONE OR TWO PROMISES DOES NOT THROW ERROR
	Promise.all([xhr, xhr2, xhr3, xhr4]).then(() => {
		console.log(loadeddata); 
		console.log(cc); //SOMETIMES CC IS NOT DEFINED (SOMETIMES IT IS)
	});
}