Method console.warn invoked with wrong context

Hi,

We’re running Autobahn JS on various terminal types, including Samsung and LG Smart TVs (Chromium-based browsers). With these Smart TVs, when the established connection is closed (for example after stopping the Crossbar server), we get JS errors like:

Uncaught TypeError: Illegal invocation

TypeError: Type error

In this case the AB connection’s onclose handler is not called, and thereby our code is not aware that reconnection must be attempted.

This issue appeared from ABJS v19.10.1. Connection handler self._transport.onclose calls:

log.warn("connection closed", reason, details);

https://github.com/crossbario/autobahn-js/blob/v19.10.1/packages/autobahn/lib/connection.js#L343

The log module defines its warn method as a direct reference to DOM console.warn:

var warn = console.warn;
exports.warn = warn;

https://github.com/crossbario/autobahn-js/blob/master/packages/autobahn/lib/log.js#L23

Execution of AB’s log.warn does not cause issue on desktop browsers (Chrome, Firefox, Edge, IE11). However it fails on the affected Smart TVs because the warn Function is executed with a this context which is not the console object. The Smart TV browsers may have a specific behaviour requiring this context (like redirecting the browser logs to an internal debugging system…).

To work on such platforms, Autobahn log module code should be something like:

var warn = console.warn.bind(console);

Note: AB’s log.debug method should not be affected by this issue, as its code uses the console context.

Beyond the specific case of these Smart TV platforms, from a more general OOP point of view, the method of an object’s instance should not be called outside of the context of this instance.

Thanks

[om26er]

@vla74 @hmistry-lz I have released autobahn-js 20.4.1, with contains the fix for this bug as well. Kindly try that.

[vla74]

You’re welcome.

1. After enabling the AB debug mode, I confirm that log.debug does not cause any exception on the affected Smart TVs, while log.warn does.
2. Yes. In more details, I tested the 2 following fixes with the affected terminals, and both work:

• Compact version with bind:

var warn = console.warn.bind(console);

• Closure similar to the declaration of the debug function:

var warn = function () {
    console.warn.apply(console, arguments);
};

Function.prototype.bind normally requires an ECMAScript 5 compatible browser (http://kangax.github.io/compat-table/es5/#test-Function.prototype.bind), however I think that there’s a polyfill embedded in ABJS (https://github.com/crossbario/autobahn-js/blob/master/packages/autobahn/lib/polyfill/function.js).

BTW, for the sake of consistency, let me suggest that debug and warn functions are declared the same way (so, probably using the bind method for both).