Perform multiple async operations at once and handle the data when everything is finished.

multiple-async.js

var toLoad = 2, // number of chunks to receive
    data = {}; // here we'll save the data, you could also use an array or multiple vars
    
$.ajax({
	url: 'a.txt',
	error: function (jqXHR, textStatus, errorThrown) {
		// handle error
	},
	success: function (dataA, textStatus, jqXHR) {
		data['a.txt'] = dataA; // so you can later access it in chunkReceived()
		chunkReceived(); // that's important
	}
});

// same, you can do this as often as you want, just make sure you change toLoad
$.ajax({
	url: 'b.txt',
	error: function (jqXHR, textStatus, errorThrown) {
		// for real, alsways handle errors!
	},
	success: function (dataB, textStatus, jqXHR) {
		data['b.txt'] = dataB;
		chunkReceived();
	}
});

function chunkReceived() {
	toLoad--;
	if (!toLoad) { // execute when all data loaded
		console.log(data['a.txt'], data['b.txt']); // example: that's how you access the data
	}
}