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function fakeAjax(url, cb) {
	var fake_responses = {
		file1: 'The first text',
		file2: 'The middle text',
		file3: 'The last text'
	};
	var randomDelay = (Math.round(Math.random() * 1e4) % 8000) + 1000;

	console.log('Requesting: ' + url);

	setTimeout(function() {
		cb(fake_responses[url]);
	}, randomDelay);
}

function output(text) {
	console.log(text);
}

// **************************************

function getFile(file) {
	var text, fn;
	fakeAjax(file, function(response) {
		if (fn) fn(response);
		else text = response;
	});

	var thunk = function(cb) {
		if (text) cb(text);
		else fn = cb;
	};

	return thunk;
}

var th1 = getFile('file1');
var th2 = getFile('file2');
var th3 = getFile('file3');

th1(function(text1) {
	output(text1);
	th2(function(text2) {
		output(text2);
		th3(function(text3) {
			output(text3);
			output('Completed');
		});
	});
});