add fetch polyfill

frontend/src/request.js

@@ -1,5 +1,35 @@
 import { getItem } from "./storage";
 
+export function compatibleFetch(endpoint, options) {
+    if (window.fetch && typeof window.fetch === "function") {
+        return fetch(endpoint, options);
+    } else {
+        return new Promise((resolve, reject) => {
+            const req = new XMLHttpRequest();
+            req.addEventListener("load", () => {
+                resolve({
+                    status: req.status,
+                    ok: [200, 201, 204].includes(req.status),
+                    json() {
+                        return JSON.parse(req.responseText);
+                    }
+                });
+            });
+            req.addEventListener("error", (e) => {
+                reject(e);
+            });
+    
+            req.open(options.method || "GET", endpoint);
+            if (options.headers) {
+                for (const [header, value] of Object.entries(options.headers)) {
+                    req.setRequestHeader(header, value);
+                }
+            }
+            req.send(options.body);
+        });
+    }
+}
+
 export default async function(method, endpoint, auth=true, body=null) {
     const options = {
         method,  
@@ -24,7 +54,7 @@ export default async function(method, endpoint, auth=true, body=null) {
     }
 
     try {
-        const res = await fetch(endpoint, options);
+        const res = await compatibleFetch(endpoint, options);
         return {
             success: true,
             json: res.status === 204 ? null : await res.json(),

frontend/src/storage.js

@@ -1,5 +1,5 @@
 const defaults = {
-    "server:apiBase": `${window.location.origin}/api/v1`,
+    "server:apiBase": `${window.location.origin || ""}/api/v1`,
     "server:gatewayBase": `${location.protocol === "https:" ? "wss" : "ws"}://${location.host}/gateway`,
     "auth:token": "",
     "ui:doAnimations": true,