__extends fails to inherit static symbols

[dpogue]

TypeScript Version:
1.8.7

Code

// A self-contained demonstration of the problem follows...
const test = Symbol('name');

class Foo {
    constructor() {
        console.log('Foo constructor');
    }
}

Foo[test] = 'testing a symbol';

class Bar extends Foo {
    constructor() {
        super();
        console.log('Bar constructor');
    }
}

let b = new Bar();
console.log(Bar[test]);

Expected behaviour:
Should output

Foo constructor
Bar constructor
testing a symbol

Actual behaviour:
Actual output is

Foo constructor
Bar constructor
undefined

This is because the __extends helper uses hasOwnProperty to check for properties to be copied over. Symbols are not properties, so they are never copied.

This works correctly with native ES6 classes, and with Babel's _inherits helper (using Object.setPrototypeOf rather than copying properties manually).