Promise version answer to the EloquentJavascript Exercise 20.1

get_authors.js

var http = require("http");
var Promise = require("promise");

function getAuthor(type) {
	return new Promise(function(resolve, reject) {
		var request = http.request({
		  hostname: "eloquentjavascript.net",
		  path: "/author",
		  method: "GET",
		  headers: {Accept: type}
		}, function(response) {
			if (response.statusCode < 200 || response.statusCode >= 300)
				return reject(new Error('status code=' + response.statusCode));

			var body = [];
			response.on('data', function(chunk) {
				body.push(chunk);
			});
			response.on('end', function() {
				resolve("Type " + type + ": " + Buffer.concat(body).toString());
			});
		});
		request.end();
	});
}

var types = [
	"text/plain",
	"text/html",
	"application/json"
];

types.map(getAuthor).reduce(function(sequence, typePromise) {
	return sequence.then(function() {
		return typePromise;
	}).then(function(body) {
		console.log(body);
	});
}, Promise.resolve());