incorrect this and class instance with inheritation

[e-cloud]

TypeScript Version: 2.1.0-dev.20161107

Code

{
 ...
 "compilerOptions": {
 "target": "es5"
 }
 ...
}

class WebpackOptionsValidationError extends Error {
 constructor() {
 super();
 Error.captureStackTrace(this, WebpackOptionsValidationError);
 this.name = 'WebpackOptionsValidationError';
 }
}

Expected behavior:

const err = new WebpackOptionsValidationError()
err instanceof WebpackOptionsValidationError // true

transpiled:

__extends(WebpackOptionsValidationError, _super);
function WebpackOptionsValidationError() {
 _super.call(this);
 Error.captureStackTrace(this, WebpackOptionsValidationError);
 this.name = 'WebpackOptionsValidationError';
 return this;
 // here return instance of WebpackOptionsValidationError
}

Actual behavior:

const err = new WebpackOptionsValidationError()
err instanceof WebpackOptionsValidationError
// false -- err is instanceof Error but not WebpackOptionsValidationError

transpiled:

__extends(WebpackOptionsValidationError, _super);
function WebpackOptionsValidationError() {
 var _this = _super.call(this) || this;
 Error.captureStackTrace(_this, WebpackOptionsValidationError);
 _this.name = 'WebpackOptionsValidationError';
 return _this;
 // here return instance of Error,
 // it refers to the prototype object of WebpackOptionsValidationError
}

---

The wrong behavior is result from #11846 and #11868.

[e-cloud]

Vladimir Matveev (@vladima) Mohamed Hegazy (@mhegazy) falsandtru (@falsandtru)

[falsandtru]

See #10166

[e-cloud]

falsandtru (@falsandtru) #10166 is related but not the solution.

I tried other class inheritances and it turns out the problem is not particular to Error inheritance.

see another example: (With Typescript 2.1 latest)

class CustomObject extends Object {
 constructor(message) {
 super()
 this.message = message
 }
}

const obj = new CustomObject('a')
console.log(obj instanceof CustomObject)

Expected output:

true

Actual:

false

You can try a playground demo(with Typescript 2.0.x)
Hit the run button and the console will log true which is expected

Conclusion:
this may breaks some code widely with Typescript 2.1

---

PS: One interesting thing is Babel also transpile it incorrectly

[falsandtru]

I wrote my solution in that issue.

[e-cloud]

compromising solution in #12123

[e-cloud]

Due to design limitation, close this