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]

nino-porcino (@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;
}

:)