False 'unused dependency' for asyncawait.

[jakeleventhal]

When importing asyncawait as such:
const async = require('asyncawait').async; const await = require('asyncawait').await;

It says that asyncawait is an unused dependency.

[mnkhouri]

Our parser (Babylon) is throwing an error when it encounters const await because await is a reserved word.

I can't currently think of a way to fix this issue... Here are some things that won't work:

• There is no option to "allow reserved words" in Babylon (some other JS parsers, like Acorn, seem to have such an option).
• I don't forsee us swapping out Babylon for Acorn or another parser

[jakeleventhal]

What if you built a step at the end that basically had a list of "packages to check". For each of those, if it finds, that it is unused, then it greps the project to quickly see if there is matching syntax (as i have shown in the issue ticket) and will remove it from the list of unused dependencies accordingly if it finds a match?

[mnkhouri]

Neat idea! We would need to handle lots of edge cases though, since there's lots of possible syntaxes that can be used for importing a module (e.g. let async=require( "asyncawait" ) is also valid). It's nice to have the parser handle all those edge cases for us, so I've created a new issue (#269) to revisit whether Acorn might be usable instead of Babylon.

I'm starting to think that the root issue here is that the Babylon parser has a fixed list of reserved words, no matter which ES version it is parsing. So even though using await as a variable name is valid before ES6, Babylon will throw an error (and then we don't get any information about the modules used in that particular file).

On the other hand, the Acorn parser can be configured to parse in ES5 mode, and probably would parse your file OK.

I'll do some investigation in the next couple weeks for #269

btw thanks for the issue!

[jakeleventhal]

of course, and thanks for actually maintaining this project lol. I think it wouldn't be too hard to have a list of reserved words like i mentioned and then just check the lines that appear in. if there is any line that has both
require followed by <special word>, then it will untag the dependency as 'unused'

I think that could be accomplished with some simple regexing and not require switchign from babylon to acorn

[LinusU]

This was a very interesting experience: 😆

Didn't think that would be valid.

Anyhow, I think that doing the regexing dance is bad because of a few reasons:

1. It will probably increase running time by quite much
2. It could have false positives
3. It shouldn't be needed

Switching to a better parser seems like the right thing to do.

no matter which ES version it is parsing.

I don't think that there are different versions though? My test above was in Node.js 10 which supports ES2018 🤔

I think that const async = ... should be valid in all JavaScript contexts.

[mnkhouri]

Interesting test! Node seems to treat some reserved words different than others (this is with v8):

I don't think that there are different versions though?

I think at some point, before classes were introduced to ES, you would have been able to say var class = 42 in Node. Doing that in a modern Node version will throw a SyntaxError. Node versions don't map directly to ES versions, but there's definitely some change over time

Switching to a better parser seems like the right thing to do.

I'll add some more thoughts in #269

[LinusU]

I think at some point, before classes were introduced to ES, you would have been able to say[...]

I think that class have been a reserved keyword since the beginning of JavaScript, which is why Node (or other runtimes) won't accept that as a variable name.

async and await on the other hand was added later to the spec, after the initial release, and thus had to be backwards compatible.

[jakeleventhal]

I agree, I think this issue can be closed and that the proper solution is to switch the parser.