Issue 6440 - Use long-lived connections to listen to extension events

ext/common.js

Index: ext/common.js
===================================================================
--- a/ext/common.js
+++ b/ext/common.js
@@ -74,4 +74,42 @@
         window.removeEventListener("message", listener._extWrapper, false);
     }
   };
+
+  class Port

[saroyanm, 2018/03/12 13:08:28]

I like that we have started to use javascript classes.

Irrelevant to current review: I wonder if we should have a note in the coding
style to prefer such syntactical sugar over using prototypes ?

(Or is this just a mock and we should use whatever works?)

[a.giammarchi, 2018/03/12 13:17:31]

FWIW, when needed, I prefer classes too and I think with current targets it'd be
pointless to prefer prototype over classes, specially because classes are more
powerful (i.e. can really extend builtins instead of just pretending and
failing)

[Thomas Greiner, 2018/03/13 18:24:45]

Yes, this is just a mock. We're still supporting Opera 39 which doesn't support
classes yet, unfortunately.
Since there seem to be agreement that we'd like to have the option to use
classes, I'll create a ticket for dropping support for Opera 39 to 42 so that we
can use them in production code. That may also fit nicely into the code
modernization that's going on in #6425.

[a.giammarchi, 2018/03/14 07:51:03]

AFAIK Opera 36 already supports Classes, but it's good to bump up Opera version
anyway.
https://caniuse.com/#feat=es6-class

P.S. if you had that `caniuse` script you would write `caniuse class` and see
results ;-)
https://webreflection.github.io/eyeo/utilities/caniuse

+  {
+    constructor(name)
+    {
+      this._name = name;
+    }
+
+    get name()
+    {
+      return this._name;
+    }
+
+    get onDisconnect()
+    {
+      return {
+        addListener() {}
+      };
+    }
+
+    get onMessage()
+    {
+      let name = this._name;
+      return {
+        addListener(listener)
+        {
+          window.addEventListener("message", (event) =>
+          {
+            if (event.data.type != "port" || event.data.name != name)
+              return;
+
+            listener(event.data.payload);
+          });
+        }
+      };
+    }
+  }
+  window.ext._Port = Port;
 }());