add bus class

web/static/src/ts/core/bus.ts

@@ -0,0 +1,32 @@
+type Callback = (...args: any[]) => void;
+
+interface Subscription {
+  owner: any;
+  callback: Callback;
+}
+
+export default class Bus {
+  private subscriptions: { [eventType: string]: Subscription[] } = {};
+
+  on(eventType: string, owner: any, callback: Callback) {
+    if (!this.subscriptions[eventType]) {
+      this.subscriptions[eventType] = [];
+    }
+    this.subscriptions[eventType].push({
+      owner,
+      callback
+    });
+  }
+  off(eventType: string, owner: any) {
+    const subs = this.subscriptions[eventType];
+    if (subs) {
+      this.subscriptions[eventType] = subs.filter(s => s.owner !== owner);
+    }
+  }
+  trigger(eventType: string, ...args: any[]) {
+    const subs = this.subscriptions[eventType] || [];
+    for (let sub of subs) {
+      sub.callback(...args);
+    }
+  }
+}

web/static/tests/bus_test.ts

@@ -0,0 +1,29 @@
+import Bus from "../src/ts/core/bus";
+
+describe("event bus behaviour", () => {
+  test("can subscribe and be notified", () => {
+    const bus = new Bus();
+    let notified = false;
+    bus.on("event", {}, () => (notified = true));
+    expect(notified).toBe(false);
+    bus.trigger("event");
+    expect(notified).toBe(true);
+  });
+
+  test("can unsubscribe", () => {
+    const bus = new Bus();
+    let notified = false;
+    let owner = {};
+    bus.on("event", owner, () => (notified = true));
+    bus.off("event", owner);
+    bus.trigger("event");
+    expect(notified).toBe(false);
+  });
+
+  test("arguments are properly propagated", () => {
+    expect.assertions(1);
+    const bus = new Bus();
+    bus.on("event", {}, (arg: any) => expect(arg).toBe("hello world"));
+    bus.trigger("event", "hello world");
+  });
+});