Switch from XMLHttpRequest to fetch API

src/renderer/util.ts

@@ -46,37 +46,9 @@ export class Listenable<T extends any[]> {
 	}
 }
 
-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);
+	const res = await window.fetch(url);
+	return await res.json();
 }
 
 export function nextAnimationFrame(): Promise<DOMHighResTimeStamp> {