Fix super method call in private instance method calling overridden method

[MattiasBuelens]

Q	A
Fixed Issues?	#9788
Patch: Bug Fix?	Yes
Major: Breaking Change?	No
Minor: New Feature?	No
Tests Added + Pass?	Yes
Documentation PR Link	No
Any Dependency Changes?	No
License	MIT

Previously, we transpiled the following code:

class Sub extends Base {
  #privateMethod() {
    return super.superMethod();
  }
}

to:

var _privateMethod2 = function _privateMethod2() {
  return babelHelpers.get(babelHelpers.getPrototypeOf(this), "superMethod", this).call(this);
};

This is incorrect: the lookup happens on the wrong prototype. The prototype chain of this looks something like:

this ---> Sub.prototype ---> Base.prototype ---> Object.prototype ---> null

getPrototypeOf(this) === Sub.prototype, so we look up Sub.prototype.superMethod. This may be overridden by Sub, so it's incorrect for the super call.

With this PR, the transpiled code becomes:

var _privateMethod2 = function _privateMethod2() {
  return babelHelpers.get(babelHelpers.getPrototypeOf(Sub.prototype), "superMethod", this).call(this);
};

getPrototypeOf(Sub.prototype) === Base.prototype, so we look up Base.prototype.superMethod. This is the expected method for the super call.

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/10643/

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/10643/

[MattiasBuelens]

You might want to remove the "needs triage" label on #9788, seeing that it's fixed now. 😉