feat(misskey-js): エラーを型として出力するように

packages/frontend/src/scripts/err-promise.ts

@@ -0,0 +1,18 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+
+export interface IErrPromise<TSuccess, TError = unknown> {
+	then<TResult1 = TSuccess, TResult2 = never>(onfulfilled?: ((value: TSuccess) => TResult1 | PromiseLike<TResult1>) | undefined | null, onrejected?: ((reason: TError) => TResult2 | PromiseLike<TResult2>) | undefined | null): Promise<TResult1 | TResult2>;
+
+	catch<TResult = never>(onrejected?: ((reason: TError) => TResult | PromiseLike<TResult>) | undefined | null): Promise<TSuccess | TResult>;
+}
+
+/** rejectに型付けができるPromise */
+export class ErrPromise<TSuccess, TError> extends Promise<TSuccess> implements IErrPromise<TSuccess, TError> {
+	constructor(executor: (resolve: (value: TSuccess | PromiseLike<TSuccess>) => void, reject: (reason: TError) => void) => void) {
+		super(executor);
+	}
+}