Port more code

src/PersistentPromise.ts

@@ -0,0 +1,33 @@
+export default class PersistentPromise {
+	private readonly promise: Promise<any>;
+	private promiseResolve: ((value?: any) => void) | undefined;
+	private promiseReject: ((reason?: any) => void) | undefined;
+
+	constructor(callback: (resolve: (value?: any) => void, reject: (reason?: any) => void) => void) {
+		this.promise = new Promise((resolve, reject) => {
+			callback(resolve, reject);
+			this.promiseResolve = resolve;
+			this.promiseReject = reject;
+		});
+	}
+
+	getPromise(): Promise<any> {
+		return this.promise;
+	}
+
+	resolve(value?: any): void {
+		if (this.promiseResolve) {
+			this.promiseResolve(value);
+		}
+	}
+
+	reject(reason?: any): void {
+		if (this.promiseReject) {
+			this.promiseReject(reason);
+		}
+	}
+
+	then(onfulfilled?: ((value: any) => any) | undefined | null, onrejected?: ((reason: any) => any) | undefined | null): Promise<any> {
+		return this.promise.then(onfulfilled, onrejected);
+	}
+}