Adds ability to interpolate delete operations

[flovilmart]

On parse.com, when running a beforeSave hook, if a key is unset the change is not propagated to the client.

On parse-server, we forward this change by setting the key: {__op: Delete} that is interpolated by the JS SDK as an UnsetOp.

This proposed PR will set key = undefined in those cases fixing parse-community/parse-server#1840

parse-community/parse-server#1946

[codecov-io]

Current coverage is 86.58%

Merging #289 into master will decrease coverage by <.01%

1. 15 files (not in diff) in src were modified. more
   • Misses -4
   • Hits -32
2. File src/ParseObject.js was modified. more
   • Misses 0
   • Partials 0
   • Hits -3

@@             master       #289   diff @@
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  Files            41         41          
  Lines          3852       3815    -37   
  Methods         703        636    -67   
  Messages          0          0          
  Branches        837        838     +1   
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- Hits           3336       3303    -33   
+ Misses          516        512     -4   
  Partials          0          0          

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[TylerBrock]

Greatness

[flovilmart]

We could have used null (it works right of the bat) but it's inconsistent with the undefined retuned when key is not set. Also, may cause problems with the iOS SDK as it interpolates to NSNull * and we usually don't love those.

[andrewimm]

Shouldn't break things. For compatibility reasons, I might want to bump the version to 1.9.0 for this.

[andrewimm]

Also I can't express how happy I am that we're resolving this ridiculous piece of tech debt that has plagued Cloud Code for years 💯

[flovilmart]

That should feel good to say it out loud 👍

[flovilmart]

You can bump to 1.9.0, but it's unlikely that will break backwards.

[andrewimm]

Agree it shouldn't break backwards, but I think it'd be easier to say "this functionality is fixed in SDK versions 1.9.0 and up"

[flovilmart]

Yup!

[TylerBrock]

Is there any timing on 1.9.0?

[andrewimm]

Sorry @TylerBrock I forgot we were blocking this. I can ship it tomorrow.

[TylerBrock]

no rush, i was just curious

[andrewimm]

I was already intending to ship it this evening, actually, but then I got caught up in investigating the best CDN solution.

[andrewimm]

Just released 1.9.0-rc1 as a beta release.

[andrewimm]

@TylerBrock turns out I totally f-d up that publish (late night, little sleep). I'm trying to unpublish rc1, but it should all be there under parse@1.9.0-rc2, aka parse@rc