I noticed that there isn't a flag to enable this. We should consider having a flag to warn when block-scoped variables are captured, or create a TSLint rule for it that we can use ourselves.

Don't think we should hide it under the flag:

• this is a missing bit in our ES6 compliance story that we deliberately decided to punt before.
• this is not a breaking change, code that used to compile before will continue to compile.

Adding TSLint rule for it sounds reasonable

pinging @mhegazy: can you have a look at this PR when you have time?

I don't see an example of arguments being used both inside and outside of the loop. Can you point it out to me or add one?

Can you add a test for this capturing?

class C {
    constructor(private N: number) { }
    foo() {
        for (let i = 0; i < 100; i++) {
            let f = () => this.N * i;
        }
    }
}

@DanielRosenwasser ok

@DanielRosenwasser any other comments?

👍

This is awesome!!!

With version typescript@1.8.0-dev.20151121 this example:

class C {
  constructor(private N: number) {}
  foo() {
    for (let i of [0]) {
      let f = () => i;
      this.N = f();
    }
  }
}

is not correctly transformed. (The _this binding is not created)

Thanks for the heads up @Nemikolh. I filed #5746 on your behalf.