Issue 4579, 6343 - Let errors from wrapped API calls bubble up

polyfill.js

Index: polyfill.js
===================================================================
--- a/polyfill.js
+++ b/polyfill.js
@@ -93,40 +93,46 @@
       // If the last argument is undefined, we drop it from the list assuming
       // it stands for the optional callback. We must do this, because we have
       // to replace it with our own callback. If we simply append our own
       // callback to the list, it won't match the signature of the function and
       // will cause an exception.
       if (typeof args[args.length - 1] == "undefined")
         args.pop();
 
+      let resolvePromise = null;
+      let rejectPromise = null;
+
+      func.call(object, ...args, result =>
+      {
+        let error = browser.runtime.lastError;
+        if (error && !portClosedBeforeResponseError.test(error.message))
+        {
+          // runtime.lastError is already an Error instance on Edge, while on
+          // Chrome it is a plain object with only a message property.
+          if (!(error instanceof Error))
+          {
+            error = new Error(error.message);
+
+            // Add a more helpful stack trace.
+            error.stack = callStack;
+          }
+
+          rejectPromise(error);
+        }
+        else
+        {
+          resolvePromise(result);

[kzar, 2018/02/06 09:49:24]

I wonder if it could be possible that resolvePromise or rejectPromise are called
before they are assigned.

[Manish Jethani, 2018/02/06 11:51:37]

Since the APIs we are wrapping are asynchronous, the callback cannot get called
immediately (otherwise it would be a bug in the implementation). On the other
hand, the "executor" of a promise is supposed to get called immediately by
design:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Obje...

"The executor function is executed immediately by the Promise implementation
..."

+        }
+      });
+
       return new Promise((resolve, reject) =>
       {
-        func.call(object, ...args, result =>
-        {
-          let error = browser.runtime.lastError;
-          if (error && !portClosedBeforeResponseError.test(error.message))
-          {
-            // runtime.lastError is already an Error instance on Edge, while on
-            // Chrome it is a plain object with only a message property.
-            if (!(error instanceof Error))
-            {
-              error = new Error(error.message);
-
-              // Add a more helpful stack trace.
-              error.stack = callStack;
-            }
-
-            reject(error);
-          }
-          else
-          {
-            resolve(result);
-          }
-        });
+        resolvePromise = resolve;
+        rejectPromise = reject;
       });
     };
 
     Object.defineProperty(object, name, descriptor);
   }
 
   function wrapRuntimeOnMessage()
   {