ES6 Promise version of Mithril's request function

request.mithril.js

m.request = function(xhrOptions) {
	var deferred = m.deferred()
	var serialize = xhrOptions.serialize = xhrOptions.serialize || JSON.stringify
	var deserialize = xhrOptions.deserialize = xhrOptions.deserialize || JSON.parse
	var extract = xhrOptions.extract || function(xhr) {
		return xhr.responseText.length === 0 && deserialize === JSON.parse ? null : xhr.responseText
	}
	xhrOptions.onload = xhrOptions.onerror = function(e) {
		e = e || event
		var unwrap = (e.type == "load" ? xhrOptions.unwrapSuccess : xhrOptions.unwrapError) || identity
		try {
			var response = unwrap(deserialize(extract(e.target, xhrOptions)))
			if (e.type == "load") {
				if (type.call(response) == "[object Array]" && xhrOptions.type) {
					for (var i = 0; i < response.length; i++) response[i] = new xhrOptions.type(response[i])
				}
				else if (xhrOptions.type) response = new xhrOptions.type(response)
				deferred.resolve(response);
			}
			else deferred.reject(response);
		}
		catch (e) {
			// Any exception in the onerror/onload is not part of the promise, so it should still throw to the caller
			if (e instanceof SyntaxError) throw new SyntaxError("Could not parse HTTP response. See http://lhorie.github.io/mithril/mithril.request.html#using-variable-data-formats")
			else throw e
		}
		finally {
			// I'm assuming you always want there to be an endcomputation so I'm sticking in this finally.
			if (xhrOptions.background !== true) m.endComputation()
		}
	}
	// Put a try/catch around anything that can potentially throw on function execution.
	try {
		if (xhrOptions.background !== true) m.startComputation()
		xhrOptions.url = parameterizeUrl(xhrOptions.url, xhrOptions.data)
		xhrOptions = bindData(xhrOptions, xhrOptions.data, serialize)
		ajax(xhrOptions)
	}
	catch (e) {
		// An exception in the promise's body should call the first rejection handler
		deferred.reject(e);
	}
	return deferred.promise
}