usage.js

simpleXhr({
	url: "data.php",
	timeout: 5000
})
.setRequestHeader( "foo", "bar" )
.send()
.then(function( xhr ) {
	console.log( "Success" );
	console.log( typeof xhr.response, xhr.response );
}, function( error ) {
	console.log( "Error" );
	console.log( error );
});

//========================================

xhr = simpleXhr({
	url: "data.php",
	timeout: 5000,
	headers: {
		foo: "bar"
	}
})
.send();

xhr.then(function( xhr ) {
	console.log( "Success" );
	console.log( typeof xhr.response, xhr.response );
}, function( error ) {
	console.log( "Error" );
	console.log( error );
});

setTimeout(function() {
	xhr.abort();
}, 500 );

xhr.js

// method
// username
// password
// url
function cleanXhr( options ) {
	var xhr = new XMLHttpRequest();
	xhr.open( options.method || "GET", options.url, true, options.username, options.password );

	// Set proxied properties directly on the XHR object
	cleanXhr.proxyProperties.forEach(function( property ) {
		if ( options.hasOwnProperty( property ) ) {
			xhr[ property ] = options[ property ];
		}
	});

	// Create a promise that resolves with the XHR
	var promise = new Promise(function( resolve, reject ) {
		xhr.onload = function() {
			resolve( xhr );
		};

		[ "abort", "error", "timeout" ].forEach(function( action ) {
			xhr[ "on" + action ] = function() {
				var error = new Error( action );
				error.xhr = xhr;
				error.options = options;
				reject( error );
			};
		});
	});

	// Expose the raw XHR object
	promise.xhr = xhr;

	// Proxy common methods for convenience and chaining
	cleanXhr.proxyMethods.forEach(function( method ) {
		promise[ method ] = function() {
			xhr[ method ].apply( xhr, arguments );
			return promise;
		};
	});

	return promise;
}

cleanXhr.proxyMethods = [
	"abort",
	"overrideMimeType",
	"send",
	"setRequestHeader"
];

cleanXhr.proxyProperties = [
	"timeout",
	"upload",
	"withCredentials"
];

// headers
// TODO: response parsing
function simpleXhr( options ) {
	var promise = cleanXhr( options );

	if ( !options.headers ) {
		options.headers = {};
	}

	if ( !options.headers[ "X-Requested-With" ] ) {
		options.headers[ "X-Requested-With" ] = "XMLHttpRequest";
	}

	Object.keys( options.headers ).forEach(function( header ) {
		promise.setRequestHeader( header, options.headers[ header ] );
	});

	return promise;
}