First steps towards onIncrement API

packages/common/src/emitter.ts

@@ -0,0 +1,51 @@
+import type { UnsubscribeCallback } from "@excalidraw/excalidraw/types";
+
+type Subscriber<T extends any[]> = (...payload: T) => void;
+
+export class Emitter<T extends any[] = []> {
+  public subscribers: Subscriber<T>[] = [];
+
+  /**
+   * Attaches subscriber
+   *
+   * @returns unsubscribe function
+   */
+  on(...handlers: Subscriber<T>[] | Subscriber<T>[][]): UnsubscribeCallback {
+    const _handlers = handlers
+      .flat()
+      .filter((item) => typeof item === "function");
+
+    this.subscribers.push(..._handlers);
+
+    return () => this.off(_handlers);
+  }
+
+  once(...handlers: Subscriber<T>[] | Subscriber<T>[][]): UnsubscribeCallback {
+    const _handlers = handlers
+      .flat()
+      .filter((item) => typeof item === "function");
+
+    _handlers.push(() => detach());
+
+    const detach = this.on(..._handlers);
+    return detach;
+  }
+
+  off(...handlers: Subscriber<T>[] | Subscriber<T>[][]) {
+    const _handlers = handlers.flat();
+    this.subscribers = this.subscribers.filter(
+      (handler) => !_handlers.includes(handler),
+    );
+  }
+
+  trigger(...payload: T) {
+    for (const handler of this.subscribers) {
+      handler(...payload);
+    }
+    return this;
+  }
+
+  clear() {
+    this.subscribers = [];
+  }
+}

packages/common/src/index.ts

@@ -9,3 +9,4 @@ export * from "./promise-pool";
 export * from "./random";
 export * from "./url";
 export * from "./utils";
+export * from "./emitter";

packages/common/src/utility-types.ts

@@ -68,3 +68,8 @@ export type MaybePromise<T> = T | Promise<T>;
 
 // get union of all keys from the union of types
 export type AllPossibleKeys<T> = T extends any ? keyof T : never;
+
+/** Strip all the methods or functions from a type */
+export type DTO<T> = {
+  [K in keyof T as T[K] extends Function ? never : K]: T[K];
+};