Unable to Babel

[danilopolani]

I can't transform underscore.min with Babel. I need it because, with gulp, I merge all files and then process them with babel, but with underscore it returns an error.

You can try it out here: https://babeljs.io/repl/#?babili=false&evaluate=true&lineWrap=false&presets=es2015

At the bottom of the right panel an error appears: "u is undefined".

[captbaritone]

I'm getting "Cannot read property '_' of undefined", which is different but also broken.

Which version of Underscore are you using?

I'm suspicious that this is related to #2153 which has been fixed in master, but we have not yet shipped a release that includes it.

You could try it with the version of Underscore on master (https://github.com/jashkenas/underscore/blob/master/underscore.js) and see if that resolves the issue?

Let me know what you find.

[danilopolani]

I'm using the version 1.8.3, the latest. Unfortunately, I cannot use the unminified version, because of the "require" methods not supported.

exports is not supported in the browser, you need a commonjs environment such as node.js/io.js, browserify/webpack etc

[captbaritone]

Where are you seeing the error with exports? I see that message when using the Babel website to transpile it, but the code looks fine. While Underscore references the exports variable, it first detects which environment it's in a only uses exports if it finds itself running in a node environment.

Basically, that "error" might just be Babel trying too hard to be helpful.

[rally25rs]

Edited after more research

I just noticed... The actual last line of Underscore is to invoke itself with this:

}.call(this));

However after built by Babel, the last line is changed to pass undefined:

}.call(undefined));

It seems that in ES6 modules, this is supposed to be undefined (though I'm having a hard time processing the actual ECMA specification to determine if that is true) so Babel replaces it automatically.

StackOverflow: How to stop babel from transpiling 'this' to 'undefined'

Screenshot from Babel's online interpreter:

[Kosta-Github]

I think, this is fixed with this commit: 8a847ba from @lexdene

however, there is no official release available containing this fix; the current version 1.8.3 does not contain it...