Subclass extends Error is broken

[omochi]

Summary

Subclass extends Error is broken.
If I define subclass and construct instance of it with new,
I get instance of Error but not instance of subclass.
So If I call instance method of this instance, it will crash.
And If I use instanceof operator to it, it return false.

TypeScript Version: 2.2.1

Code

// a.ts
class MyError extends Error {
    greet() {
        console.log("I am MyError!");
    }
}

let e = new MyError();
console.log(e instanceof MyError);
e.greet();

Compile and run

[omochi@omochi-MB ts-inst]$ $(npm bin)/tsc --version
Version 2.2.1
[omochi@omochi-MB ts-inst]$ node --version
v7.7.2
[omochi@omochi-MB ts-inst]$ $(npm bin)/tsc --target ES3 a.ts
[omochi@omochi-MB ts-inst]$ node a.js

Expected behavior:

Print true and I am MyError! on console.

Actual behavior:

Crash with this stacktrace.

false
/Users/omochi/temp/ts-inst/a.js:22
e.greet();
  ^

TypeError: e.greet is not a function
    at Object.<anonymous> (/Users/omochi/temp/ts-inst/a.js:22:3)
    at Module._compile (module.js:571:32)
    at Object.Module._extensions..js (module.js:580:10)
    at Module.load (module.js:488:32)
    at tryModuleLoad (module.js:447:12)
    at Function.Module._load (module.js:439:3)
    at Module.runMain (module.js:605:10)
    at run (bootstrap_node.js:425:7)
    at startup (bootstrap_node.js:146:9)
    at bootstrap_node.js:540:3

My investigation

I tested this with some other configuration.

tsc version	target version	result
2.0.0	ES3	OK
2.0.0	ES2015	OK
2.2.1	ES3	NG
2.2.1	ES2015	OK
2.3.0-dev.20170316	ES3	NG
2.3.0-dev.20170316	ES2015	OK

What attract me is |2.0.0|ES3|OK|.

With 2.0.0, compiled constructor is below.

var MyError = (function (_super) {
    __extends(MyError, _super);
    function MyError() {
        _super.apply(this, arguments);
    }
    return MyError;
}(Error));

With 2.2.1, compiled constructor is below.

var MyError = (function (_super) {
    __extends(MyError, _super);
    function MyError() {
        return _super !== null && _super.apply(this, arguments) || this;
    }
    return MyError;
}(Error));

The difference is return value of MyError().
In 2.0.0, it returns undefined.
In 2.2.1, it returns instance from _super.apply(this, arguments) which is instance of Error but not MyError.

According what I hear, this change of constructor implementation is come from spec of ECMA2015.
But with ES2015 target compile, tsc generated raw JavaScript class syntax and It run correctly. (So compiled result javascript is almost same with source typescript)
So I think this behavior with ES3 target is bug.

[vvakame]

related: #10762

[HerringtonDarkholme]

https://github.com/Microsoft/TypeScript/wiki/FAQ#why-doesnt-extending-built-ins-like-error-array-and-map-work

[omochi]

@HerringtonDarkholme Thanks for information and sorry for my overlooking.
I tested this workaround and it runs expectedly.
Because earlier version 2.0.0 runs expectedly, I thought this current behavior is bug.
But I understood that this is regular result.