Error handling - no output from .on('error')

I would like to plugin my custom error handling/notifier. In my other recipes such as sass, I simply use:

.on('error', (error) => {
    this.notifyError(error, watching)
})

I see this plugin uses throw Error instead of a stream.emit('error') similar to scssLint

In order to work around this issue where #failAfterError doesn’t emit an error to my handler, I implemented a very ugly #result handler mostly duplicating #failAfterError but it will trigger my own notifier (#results fails to notify).

Note: this custom error handling attempts led me to discover to #134

I’m new to gulp, but it seems like I should be able to listen for an error based on patterns of use from other plugins. Is there any recommendation to improve this code? It seems like an unnecessary hack.

[adametry]

Note: I’ll get into a bit of detail here. So, if you just want a solution, skip to the workarounds.

Would I be right to assume that you’re referring to the throw in failOnError or failAfterError? If so, this takes advantage of a convenience provided the result and results methods (respectively). Both use the tryResultAction method to catch thrown errors and pass them to the stream (the stream’s onwrite function emits the error).

I believe some confusion may be when the error is thrown. The failAfterError method creates a results (plural) stream, which waits until it has ended (technically, the “prefinish” event) to perform it’s action once (collectively). Alternatively, the failOnError method creates a result (singular) stream, which will act (immediately) on each chunk/file. Likewise, the format method uses results, and the formatEach method uses result.

In your code, you work around the issue of failAfterError not behaving as expected by creating a result stream and use logic from the failAfterError method. In this case, you could simply use failOnError for the same effect; however, is likely end the stream before format can print lint results. You can simply use failAfterError in place of the custom result stream to emit an error after linting & printing all files.

Now, to the heart of the matter: no “error” event. It appears that the issue may be that gulp-if is muting the error emitted from failAfterError. As you demonstrate in your code, throwing in the result method results in an “error” event.

Three simple workarounds:

1. Set the “error” event listener on the failAfterError stream (rather than the stream that gulpIf returns)
2. Remove gulpIf, use results instead of result, and add !watching to its failure condition.
3. Remove gulpIf and pipe to failAfterError with the “error” listener only if !watching (be sure to return the piped stream).

On a side note, you can throw anything from a result or results method. gulp-eslint will wrap handle wrapping the thrown value in a PluginError.

[rosskevin]

This is a problem somewhere with gulp v3, I’m switching to gulp v4 and everything is working as expected, very strange indeed, but I’m going to close this as v4 is close to release and this probably isn’t worth tracking down.