feat: add onChange, onPointerDown, onPointerUp api subs (#7154)

src/emitter.ts

@@ -0,0 +1,47 @@
+type Subscriber<T extends any[]> = (...payload: T) => void;
+
+export class Emitter<T extends any[] = []> {
+  public subscribers: Subscriber<T>[] = [];
+  public value: T | undefined;
+  private updateOnChangeOnly: boolean;
+
+  constructor(opts?: { initialState?: T; updateOnChangeOnly?: boolean }) {
+    this.updateOnChangeOnly = opts?.updateOnChangeOnly ?? false;
+    this.value = opts?.initialState;
+  }
+
+  /**
+   * Attaches subscriber
+   *
+   * @returns unsubscribe function
+   */
+  on(...handlers: Subscriber<T>[] | Subscriber<T>[][]) {
+    const _handlers = handlers
+      .flat()
+      .filter((item) => typeof item === "function");
+
+    this.subscribers.push(..._handlers);
+
+    return () => this.off(_handlers);
+  }
+
+  off(...handlers: Subscriber<T>[] | Subscriber<T>[][]) {
+    const _handlers = handlers.flat();
+    this.subscribers = this.subscribers.filter(
+      (handler) => !_handlers.includes(handler),
+    );
+  }
+
+  trigger(...payload: T): any[] {
+    if (this.updateOnChangeOnly && this.value === payload) {
+      return [];
+    }
+    this.value = payload;
+    return this.subscribers.map((handler) => handler(...payload));
+  }
+
+  destroy() {
+    this.subscribers = [];
+    this.value = undefined;
+  }
+}