Enable await in expressions

[vmarkovtsev]

The implementation is copied from Node's --experimental-repl-await

Screenshot of ijavascript with this patch:

DISCLAIMER: I am a totally lame JS programmer 🤦‍♂️: I have to spend some time to figure out how to write tests for this project, how to properly integrate acorn - it is currently integrated the same way as in Node, etc. So consider this a PoC. Feel free to implement everything by yourself and close this PR (I mean, really) or bear with me to make a proper PR. In the latter case I will be grateful for your JS improvement hints and lessons 😄

[vmarkovtsev]

• Read CONTRIBUTING.md
• Added await tests
• Added the ability to skip tests based on the node version (prior to 7.6 do not have await)
• Passed CI

await.js is copied so I excluded it from eslint.

[alancnet]

+1 on this. Hope to see this merged, and mine closed.

[n-riesco]

@vmarkovtsev @alancnet Sorry for the silence. I've had a quick read, but I haven't had a chance to test this PR.

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I've just had an idea while thinking about this PR: I'd like to test if it's possible to replace this PR with a PR that adds the flag --experimental-repl-await to this line.

[vmarkovtsev]

@n-riesco I've already tried that but it did not work for me. The reason is that this flag works only in the REPL mode.

[vmarkovtsev]

ping

[n-riesco]

@vmarkovtsev apologies for the silence. I'll work on this tomorrow.

[n-riesco]

@vmarkovtsev I've moved this PR to a branch of the IJavascript repository. For the time being, I'm distributing this branch in the package ijavascript-await (I did something similar with jmp and jmp-prebuilt when we were testing the transition from zmq to the prebuilt binaries of zeromq).

I'm also distributing lib/server/await.js as package jp-parser. The main reason for this is to keep NEL free of external dependencies.

Ideally, I'd like this functionality to be part of Node.js (I'll explore what is needed at some point in the future). I don't want to go down the route where IJavascript reimplements Node.js.

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@vmarkovtsev I'd like to give you credit for your contribution here. Please, would you have a look at the branch I created in the IJavascript repository? And if you're happy, please would create a PR against that branch to update the file AUTHORS with your details?

[vmarkovtsev]

@n-riesco Sure, as long as it works I am fine 😄 n-riesco/ijavascript#172

[n-riesco]

@vmarkovtsev Your tests are passing 😉!

@alancnet

For anyone wanting to test IJavascript with global await expressions, please, note that for the time being I'm distributing this feature in the packageijavascript-await:

npm install -g ijavascript-await

[vmarkovtsev]

Thanks!