fix choosing maps

tank-frontend/src/MapDropDown.tsx

@@ -0,0 +1,28 @@
+import { ChangeEvent, useEffect, useState } from "react";
+import { getMaps, postMaps } from "./serverCalls";
+
+export default function MapDropDown() {
+    const [mapList, setMaps] = useState<string[] | null>(null);
+
+    useEffect(() => {
+        let aborted = false;
+        async function startFetch() {
+            const response = await getMaps();
+            if (!aborted && response.ok && response.successResult)
+                setMaps(response.successResult);
+        }
+        startFetch();
+        return () => { aborted = true };
+    }, []);
+
+    const onChange = (event: ChangeEvent<HTMLSelectElement>) => {
+        postMaps(event.target.options[event.target.selectedIndex].value);
+        event.preventDefault();
+    };
+
+    return <select value="maps" className='DropDown' onChange={onChange}>
+        <option value="" defaultValue={""} >Choose map</option>
+        {mapList?.map(m =>
+            <option key={m} value={m}>{m}</option>)}
+    </select>
+}