`idx` should be implemented such that function calls don't lose their `this` binding

[steveluscher]

This doesn't work:

componentWillUnmount(): void {
  idx(this.foo, _ => _.bar());
  delete this.foo;
}

It gets transformed to this:

(_ref = this.foo) != null 
  ? (_ref = _ref.bar) != null 
    ? _ref() 
  : _ref 
: _ref;
delete this.foo;

And can throw this kind of error because internal to foo, this is undefined:

TypeError: Cannot read property '_baz' of undefined

This works fine:

componentWillUnmount(): void {
  if (this.foo) {
    this.foo.bar();
  }
  delete this.foo;
}

I suppose idx should do this instead?

(_ref = this.foo) != null 
  ? _ref.bar != null
    ? _ref.bar() 
  : _ref.bar 
: _ref;

Minimal test case: (link)

[steveluscher]

Just for posterity, I hand coded this bug into idx in the first place.

[yungsters]

Obsoleted in 2.0.0.