Prevent ungettable objects from getting gotten during path lookup

[pittst3r]

This is a follow-up to #13449.

It was observed by @krisselden that doing something like the following…

Ember.get({ foo: 42 }, 'foo.bar');

… would eventually call get internally like…

get(42, 'bar');

… which is no bueno.

To generalize, we should only call get from _getPath with objects (except null), functions, and strings. I'm also wondering if we should add a deprecation to warn people when they do something like…

Ember.get(42, 'bar');

… so we can eventually add an assertion. Right now that will just return undefined.

[krisselden]

move to const outside the function

[krisselden]

also can just be an object literal with 1s

[rwjblue]

like:

const ALLOWABLE_TYPES = {
  object: true,
  function: true,
  string: true
}

[pittst3r]

Will do. Thanks, guys.

[pittst3r]

Just pushed the update. In the update I am casting undefined into false, so let me know if you believe that to be superfluous and I will remove.

[krisselden]

I think @mmun wanted a test for obj = { str: '' }; strictEquals(get(obj, 'str.length'), 0);

[pittst3r]

There's already one here, but now that I'm looking at it again it's only equal and not strictEqual. I can update that.

[pittst3r]

K, strictEqual added. 👍

[rwjblue]

I don't think the explicit coercion is needed here. It is probably fine either way though...

[pittst3r]

Just pushed the update for this.

[krisselden]

This looks good, though, this is cleanup, not really a BUGFIX.