this reference in Object

[senyaak]

TypeScript Version: 1.8.0 / nightly (2.0.0-dev.201xxxxx)

Code

interface IFoo {
  get(val: number): number;
  getAll(val: string): number;
}
function foo(): IFoo {

  return {
    get(val: number): number {
      return val + 1;
    },
    getAll(val: string): number {
      return this.get(val)*10;
    }
  };
}

Expected behavior:
Compiler show an error that val string isn't a number
Actual behavior:
No error.

Trick to get expected behavior:

interface IFoo {
  get(val: number): number;
  getAll(val: string): number;
}
function foo(): IFoo {

  var a: IFoo =  {
    get(val: number): number {
      return val + 1;
    },
    getAll(val: string): number {
      return this.get(val)*10;
    }
  };

  return a;
}

[nippur72]

it seems correct to me as this.get() does not refer to the get() defined in the object, but to a whatever get function that appears in this context when the function will be called.

Try writing this way:

interface IFoo {
  get(val: number): number;
  getAll(val: string): number;
}
function foo(): IFoo {
  const get = function(val: number): number {
      return val + 1;
  };
  const getAll = function(val: string): number {
      return get(val)*10;
  } 
  return {
    get, getAll
  };  
}

And btw, your "Trick to get expected behavior" does not works neither.

[danielearwicker]

See #6739 for work in this area, though I don't think all of it is going into 2.0.

[RyanCavanaugh]

@nippur72 's comment is correct. You can use an arrow function to actually preserve this, or an explicit this type annotation (in TS 2.0) if somehow people are invoking a with your class instance as this (how??)

[senyaak]

sorry Trick to get expected behavior should be:

interface IFoo {
  get(val: number): number;
  getAll(val: string): number;
}
function foo(): IFoo {

  var a: IFoo =  {
    get(val: number): number {
      return val + 1;
    },
    getAll(val: string): number {
      return a.get(val)*10;
    }
  };

  return a;
}

:)