Add local dir

js/Disposable.ts

@@ -2,12 +2,27 @@ type Teardown = (() => void) | { dispose: () => void };
 
 export default class Disposable {
   _teardowns: Teardown[] = [];
+  disposed: boolean;
+
+  constructor() {
+    this.disposed = false;
+  }
 
   add(...teardowns: Teardown[]): void {
+    if (this.disposed) {
+      throw new Error(
+        "Attempted to add a new teardown to a disposed disposable."
+      );
+    }
     this._teardowns.push(...teardowns);
   }
 
   dispose() {
+    if (this.disposed) {
+      throw new Error(
+        "Attempted to dispose disposable which is already disposed."
+      );
+    }
     this._teardowns.forEach(teardown => {
       if (typeof teardown === "function") {
         teardown();
@@ -15,5 +30,6 @@ export default class Disposable {
         teardown.dispose();
       }
     });
+    this.disposed = true;
   }
 }

js/actionCreators/milkdrop.ts

@@ -42,6 +42,12 @@ export function initializePresets(presetOptions: any): Dispatchable {
   };
 }
 
+export function appendPresetFileList(presets: FileList[]): Dispatchable {
+  return async dispatch => {
+    dispatch({ type: GOT_BUTTERCHURN_PRESETS, presets });
+  };
+}
+
 export function selectNextPreset(): Dispatchable {
   return (dispatch, getState) => {
     const state = getState();

js/components/MilkdropWindow/PresetOverlay.tsx

@@ -161,6 +161,16 @@ class PresetOverlay extends React.Component<Props, State> {
     }
   };
 
+  async loadLocalDir() {
+    const fileReferences = await promptForFileReferences({ directory: true });
+    if (this._disposable.disposed) {
+      return;
+    }
+    // TODO: Technically there is a race condition here, since the component
+    // could get unmounted before the promise resolves.
+    this.props.loadPresets(fileReferences);
+  }
+
   render() {
     const { height, width } = this.props;
     if (this.props.presetKeys == null) {