Adding custom check function for await store

src/awaiter.ts

@@ -1,5 +1,7 @@
 import Observable, { ObserverCallback } from "./observable";
 
+export type CheckFunction<T> = (val: T) => boolean;
+
 export default class AwaitStore<T = any> {
    private observable = new Observable<T>();
    constructor(private _value: T) {
@@ -49,7 +51,7 @@ export default class AwaitStore<T = any> {
     * @param val Value to await
     */
    awaitValue(
-      val: T
+      val: T | CheckFunction<T>
    ): PromiseLike<void> & {
       catch: (cb: (err: any) => PromiseLike<void>) => PromiseLike<void>;
       ignore: () => void;
@@ -58,7 +60,12 @@ export default class AwaitStore<T = any> {
 
       let prms = new Promise<void>((yes) => {
          const cb = () => {
-            if (this._value === val) {
+            if (typeof val === "function") {
+               if ((val as CheckFunction<T>)(this._value)) {
+                  yes();
+                  this.unsubscribe(cb);
+               }
+            } else if (this._value === val) {
                yes();
                this.unsubscribe(cb);
             }