Add --es6 option to enable ES6 compliant syntax

[danielkhan]

This PR

• adds a new --es6 flag to enable ES6 (ES2015) syntax
• replaces const with var if --es6 is set
• adds string templates if --es6 is set
• prefers arrow functions for callbacks if --es6 is set
• makes sure that this feature is only available for Node.js >= 6.0.0
• adds tests for --es6

Reference Link #167

[danielkhan]

Is there a chance to land this one? I'll be creating an online course in August and ideally I'd like to use the new feature there.

[alieslamifard]

@danielkhan it's better to validate your code with eslint(airbnb-es6). there is some issue with app.js and www.js file.

[danielkhan]

@alieslamifard are you referring to the result? Right now, the resulting code is not fully airbnb compatible as the non-es6 code wasn't as well. To not fix too much within one PR, this wasn't done deliberately.

[yardenshoham]

Yes, I have not gotten around to getting all the 4.17 stuff sorted out in the generator yet. Having PRs like thus one with merge conflicts also slows this down, as I want to get all these things into said 4.17 release so they do not wait again for who knows how long. Not having merge conflicts that I have to resolve is always a big help, though, if someone would like to resolve them on this PR.

How would one be able to resolve the conflicts? I'm new to this and can't find the conflicts (only that they're in test/cmd.js).

[dougwilson]

Likely only OP or myself can. I will do it when I get around to it, of course. This is just one of the many things on my todo list and I'm not even in my own country right now to do any work anyway.

[danielkhan]

@dougwilson - I think it's hard to prevent conflicts when PRs are sitting for such a long time.
I just resolved the conflict. Let me know if I can help.

[dougwilson]

Thank you. Looks like just need to run "npm run lint" to fix the linting errors and it should be good to go, as that is the only thing failing on CI.

[dougwilson]

There also seems to be a stray error: unknown option '--es6' printed during the tests if it is possible to hide that.

[dougwilson]

P.S. I wanted to add that I am just listing out the things I would look into / modify when landing the PR. You are not required to do anything, as I will do it when landing. Just wanted to state that because I have had people rage close their PR when I was just trying to list the things I would do since they wanted it to land faster. I would prefer that did not happen here and if you feel like not making further changes I will do them no problem.

[danielkhan]

@dougwilson - fixed linting problems. Console output is gone.

[backendsuraj]

When will this PR get merged with master?

[dougwilson]

Ok, I am locking this as apparently people are going to keep asking the same question endlessly.