Link-Completion-Events

function connectAccount(url) {
  // Derive the origin from the URL you were given rather than hard-coding one:
  // if your account uses its own linking domain, the popup runs on that.
  const popupOrigin = new URL(url).origin;

  const popup = window.open(url, "ayrshare-connect", "width=600,height=800");
  if (!popup) {
    handleOutcome({ event: "connect:error", message: "The popup was blocked." });
    return;
  }

  // Declared before anything can call `cleanup`: a message arriving early would
  // otherwise hit `poll` in its temporal dead zone and throw.
  let poll;

  const cleanup = () => {
    clearInterval(poll);
    window.removeEventListener("message", onMessage);
  };

  const onMessage = event => {
    // Both checks, not just the origin: another tab or frame on the same origin
    // could otherwise post a message your handler would believe.
    if (event.origin !== popupOrigin || event.source !== popup) return;
    const message = event.data;
    if (!message || message.source !== "ayrshare") return;

    if (["connect:success", "connect:error", "connect:cancelled"].includes(message.event)) {
      // `finally`, so your own handler throwing cannot leave the poll running —
      // it would later see the closed popup and report `cancelled` on top of the
      // outcome you already had. Cleanup also matters after `connect:error`,
      // where the popup stays open so your user can read it.
      try {
        handleOutcome(message);
      } finally {
        cleanup();
      }
    }
  };
  window.addEventListener("message", onMessage);

  // A hand-closed popup sends nothing, so watch for it. Wait a moment before
  // deciding: the popup closes itself right after sending, and the message can
  // still be in flight when you first see the window go.
  let closedAt = null;
  poll = setInterval(() => {
    if (!popup.closed) return;
    if (closedAt === null) {
      closedAt = Date.now();
      return;
    }
    if (Date.now() - closedAt < 750) return;

    cleanup();
    handleOutcome({ event: "connect:cancelled", reason: "popupClosed" });
  }, 500);
}