Generating super(...arguments) in constructor

[yulianovdey]

Hello!

MR #10189 is causing an issue after I compile TypeScript with target set to es6 and run it through Babel using babel-preset-es2015-node4.

You can find a repro here. Test by running npm i && npm run compile && node dist/test.js. To summarize, the following code:

abstract class Base {
  public abstract myProperty: string;
}

class Child extends Base {
  myProperty = 'A value';
}

Results in an error:

super(...arguments);
      ^^^
SyntaxError: Unexpected token ...

Caused by the fact that spread is still being used in the constructor:

class Child extends Base {
    constructor() {
        super(...arguments);
        this.myProperty = 'A value';
    }
}

Not touching arguments is deliberate behavior on Babel's part, so I'm wondering if there is a way to make the change in #10189 more compatible with Node 4 without having to transpile to es5.

[DanielRosenwasser]

@kittens @chancancode - I'm not sure why arguments is specifically not being touched here.

[mhegazy]

this is valid ES6 code. spread operator is allowed on arguments as well. not sure how transforming the rest of the ES6 expressions but leaving ...arguments would be ok.

#10175 was mainly done to address emit quality for babel. i will let @chancancode reply.

[chancancode]

Yes, it is valid ES6 code.

Since Babel has the ability to parse/compile that down to ES5 (meaning it understands the native syntax, and knows what to do if it decides the target platform doesn't support the native syntax), it seems like a bug in the babel-preset-es2015-node4 preset?

[yulianovdey]

Thank you for your input guys. I found a relevant issue that was opened with Babel, maybe someone can provide more info there.

[yulianovdey]

I was able to get some clarification on the Babel Slack. Usingtransform-es2015-classes seems to a requirement in this case because super is not a function and requires native spread.

Thanks again!