simple script to test support for BroadcastChanel and MessageChannel across node/bun/deno

channels_support.ts

/**
 * Simple feature‑detection helpers
 * (exported so test code can get 100 % coverage).
 */
export const hasBroadcastChannel = (): boolean =>
  typeof globalThis.BroadcastChannel === "function";

export const hasMessageChannel = (): boolean =>
  typeof globalThis.MessageChannel === "function";

/**
 * Demo / CLI entry‑point
 */
export async function runDemo(): Promise<void> {
  console.log(`BroadcastChannel supported: ${hasBroadcastChannel()}`);
  console.log(`MessageChannel   supported: ${hasMessageChannel()}`);

  // ─── Send a smoke‑test message through each channel ──────────────────────────
  if (hasBroadcastChannel()) {
    const bc = new BroadcastChannel("demo");
    bc.onmessage = (e) => console.log("BroadcastChannel received ▶", e.data);
    bc.postMessage("hello from BroadcastChannel");
    // allow the event loop one turn so we actually receive the message
    await new Promise((r) => setTimeout(r, 0));
    bc.close();
  }

  if (hasMessageChannel()) {
    const { port1, port2 } = new MessageChannel();
    port1.onmessage = (e) => console.log("MessageChannel received ▶", e.data);
    port2.postMessage("hello from MessageChannel");
    await new Promise((r) => setTimeout(r, 0));
    port1.close();
    port2.close();
  }
}

// When run via `deno run channels_support.ts`
if (import.meta.main) await runDemo();