Add support for serializing ES6 sets & maps

[pimterry]

This fixes #12

It's fairly simple: the map/set contents are serialized as arrays (using map.entries() or set.values()), which can be passed straight back to their constructor to reconstitute them, and the map/set contents are recursively serialized in turn with an extra call to serialize (passing the same options).

Note that this requires Array.from. That means it doesn't work in IE, or in Node < 4. Map/Sets are only available in IE11+ though, and Node 0.12+, so there's a very small set of environments where you could actually hit that, and judging from your current test setup that's acceptable.

If Map/Set serialization is needed in those environments it just needs an Array.from polyfill.

[yahoocla]

Thank you for submitting this pull request, however I do not see a valid CLA on file for you. Before we can merge this request please visit https://yahoocla.herokuapp.com/ and agree to the terms. Thanks! 😄

[pimterry]

(Doesn't seem to have updated, but I have now signed the CLA)

[okuryu]

Thanks! It looks good to me.

[pimterry]

If you're happy with it then @okuryu, can we merge and release this? Anything else that needs doing first? Let me know if there's any way I can help.

[okuryu]

Sorry for delay! I'll work on this in this week!

[okuryu]

I have only one concern. Regarding Array.from isn't supported on IE11, I would like to avoid use it if possible. I'm worried that the same problem may recur as there was a report (#41) in the past for ES5 compatibility. If we accept this change, we might need to change the version to v2.0.0. Thought?

[pimterry]

It's less risky than the arrow function issue, because this is just using a new function, not new syntax. You should never hit issues with generic minification or linting tools as in #41 - it's only at runtime, and only if you're using IE11 and you're serializing Map/Set objects and you're not using any modern polyfills. The support is much better than arrow functions too: arrow function support starts at Node 6, while this works for Node 0.12+.

If you do want to fix it, there's a few options. .entries() and .values() always return an iterator, so you need some way to convert that to an array. You could include a standard Array.from polyfill, but it's a little messy. Alternatively we could build our own simplified polyfill here, that only supports this one iterator case, but then you're maintaining your own unique polyfill.

Option 3, we could just document it more explicitly. How would you feel if I just added the below to the docs?

Please note that serialization for Sets & Maps requires support for Array.from (not available in IE or Node < 0.12), or an Array.from polyfill.

[okuryu]

Okay, let's take your option 3. Would you mind tweaking the README?

[pimterry]

@okuryu sure, done 👍

[okuryu]

Thanks! 👍

[okuryu]

Published serialize-javascript@1.7.0. Thanks!

[pimterry]

Amazing, thank you!