[FEATURE ember-metal-ember-assign] Introduce Ember.assign()

[tricknotes]

Ember.assign() is discussed in #11978 .

• Add feature flagging for the API addition
• Add a test for the deprecation of Ember.merge when the flag is enabled
• Add some cursory tests for ember-metal/assign (doesn't need to be complicated, but I noticed no tests were tweaked/changed for merge or assign and figured we probably want some to exist).
• We should use Object.assign if it exists (making our Ember.assign a straight up polyfill).

[rwjblue]

I think we will need to feature flag the public API change.

[rwjblue]

Could you:

• Add feature flagging for the API addition
• Add a test for the deprecation of Ember.merge when the flag is enabled
• Add some cursory tests for ember-metal/assign (doesn't need to be complicated, but I noticed no tests were tweaked/changed for merge or assign and figured we probably want some to exist).

[rwjblue]

Another point made in #12320 (that I agree with) is that we should use Object.assign if it exists (making our Ember.assign a straight up polyfill).

[rwjblue]

@tricknotes - I moved the various comments/todo items into a checklist in the PR description (so you can check them off as you go).

[tricknotes]

Sorry for my late :<
Thanks @rwjblue . Yes, I'm agree with these todo checklist!

I'll continue to work in this weekend.

[oriSomething]

if there is a well known and widely use of a polyfill, why writing a code for it and not using it?

[tricknotes]

if there is a well known and widely use of a polyfill, why writing a code for it and not using it?

I think Ember.assign is enough to work just merge some objects. It might not required to be strict as Object.assign.

[tricknotes]

@rwjblue
All todo things are done.
Could you review again?

[rwjblue]

@tricknotes - Looks great, can you squash commits and make the new commit's title [FEATURE ember-metal-ember-assign]?

[tricknotes]

Thanks, @rwjblue .
done.

[rwjblue]

Awesome work as usual, thank you @tricknotes!

[oriSomething]

@tricknotes @rwjblue i think if Ember.assign is supposed to be a polyfill when there is no Object.assign, it suppose to support also copying of Symbols as Object.assign does.

There are versions of chrome that support Symbol but no Object.assign, so need is exist.

[rwjblue]

We are not intending to make a full fidelity polyfill here, just the behaviors that we need. If you need/want a full polyfill you should include a full fidelity version (like the one you linked) and that will be used instead (since it actually sets Object.assign).

[oriSomething]

@rwjblue but three things:

• it might lead to confusion. there are still browsers that support Symbols and not Object.assign if it's not a polyfill, why naming as one and more over use Object.assign when available? better left with merge and prevent confusion
• it will lead to unexpected behavior, maybe is seems like very edge case because Symbols are not in a wide usage, be it still might cause a bugs and unexpected behaviors in some browsers. specially in future where more people will use them, and more mobile phone with various mobile browsers
• it's only a few lines of code to add to support Symbols and make it a full polyfill. much shorter than this comment

i know it sounds picky and very edge case, but as web developers we all fight very edge cases everyday. and many don't know enough Ember nor Object.assign and we might cause them many trouble for so little code. in the bottom we better not use it as a polyfill or fully polyfill this feature