From 3398070e26586164218d17a20b91bf6428902396 Mon Sep 17 00:00:00 2001
From: Jonas Jenwald <jonas.jenwald@gmail.com>
Date: Wed, 17 Feb 2021 15:52:01 +0100
Subject: [PATCH] [api-minor] Remove support for synchronous event dispatching
 in `LoopbackPort`

*Please note:* The `defer` parameter has been enabled by default ever since PR 9777 (in 2018), which first shipped in PDF.js release `2.0.943`.
With workers *disabled*, e.g. in Node.js environments, this has been used ever since without any problems reported[1].

The impetus for this change was that I happened to notice that *if* the `LoopbackPort` was used with synchronous event dispatching, we'd simply send that data as-is to the listeners. This created an inconsistency in the data returned from the `pdf.worker.js` file, since `postMessage` used with *actual* workers (or the `LoopbackPort` with `defer = true`) will ignore/throw when encountering unclonable data.
Originally my intention was simply to just call `cloneValue` regardless of the event dispatching used in `LoopbackPort`, however looking at the use-cases (or lack thereof) of the `LoopbackPort` it seemed reasonable to simply remove the `defer` parameter instead.

This patch is tagged "[api-minor]" since the `LoopbackPort` is still exposed in the API, although I really hope that no third-party is using this (since disabling workers leads to bad performance).

Finally, this patch changes a `forEach` loop to `for...of` and makes uses of optional changing in existing code.

---
[1] As evident by the `npm test` command run by Github Actions, and previously by Travis.
---
 src/display/api.js | 21 +++++++--------------
 1 file changed, 7 insertions(+), 14 deletions(-)

diff --git a/src/display/api.js b/src/display/api.js
index c8c5c025b..9339e5bc7 100644
--- a/src/display/api.js
+++ b/src/display/api.js
@@ -1624,9 +1624,8 @@ class PDFPageProxy {
 }
 
 class LoopbackPort {
-  constructor(defer = true) {
+  constructor() {
     this._listeners = [];
-    this._defer = defer;
     this._deferred = Promise.resolve(undefined);
   }
 
@@ -1670,7 +1669,7 @@ class LoopbackPort {
           continue;
         }
         if (typeof desc.value === "function") {
-          if (value.hasOwnProperty && value.hasOwnProperty(i)) {
+          if (value.hasOwnProperty?.(i)) {
             throw new Error(
               `LoopbackPort.postMessage - cannot clone: ${value[i]}`
             );
@@ -1682,19 +1681,13 @@ class LoopbackPort {
       return result;
     }
 
-    if (!this._defer) {
-      this._listeners.forEach(listener => {
-        listener.call(this, { data: obj });
-      });
-      return;
-    }
-
     const cloned = new WeakMap();
-    const e = { data: cloneValue(obj) };
+    const event = { data: cloneValue(obj) };
+
     this._deferred.then(() => {
-      this._listeners.forEach(listener => {
-        listener.call(this, e);
-      });
+      for (const listener of this._listeners) {
+        listener.call(this, event);
+      }
     });
   }