Promisify XMLHttpRequest

src/index.ts

@@ -1,23 +1,17 @@
 import MapData from './model/data/MapData';
 
+import { getJSON } from './util';
 import { loadMap } from './view/map';
 import Renderer from './view/renderer/Renderer';
 
-window.onload = () => {
+window.onload = async () => {
 	const canvas = document.getElementById('rpgedit') as HTMLCanvasElement;
 	if (!canvas)
 		return;
 
 	const renderer = new Renderer(canvas);
 
-	const xhr = new XMLHttpRequest();
+	const map = new MapData(await getJSON('resources/map/test.json'));
-
+	const mapView = await loadMap(renderer, map);
-	xhr.addEventListener('load', async function() {
+	mapView.render();
-		const map = new MapData(JSON.parse(this.responseText));
-		const mapView = await loadMap(renderer, map);
-		mapView.render();
-	});
-
-	xhr.open('GET', 'resources/map/test.json', true);
-	xhr.send();
 };

src/util.ts

@@ -45,3 +45,36 @@ export class Listenable<T extends any[]> {
 		this.listeners.forEach((l) => l(...args));
 	}
 }
+
+export function get(url: string): Promise<XMLHttpRequest> {
+	return new Promise((resolve, reject) => {
+		const xhr = new XMLHttpRequest();
+
+		const handleError = () => {
+			if (xhr.readyState !== xhr.DONE) {
+				reject(new Error('HTTP request ended in state ' + xhr.readyState));
+				return;
+			}
+
+			reject(new Error('HTTP request returned status ' + xhr.status));
+		};
+
+		xhr.addEventListener('error', handleError);
+
+		xhr.addEventListener('load', () => {
+			if (xhr.readyState !== xhr.DONE || xhr.status !== 200) {
+				handleError();
+				return;
+			}
+
+			resolve(xhr);
+		});
+
+		xhr.open('GET', url, true);
+		xhr.send();
+	});
+}
+
+export async function getJSON(url: string): Promise<any> {
+	return JSON.parse((await get(url)).responseText);
+}