A Typed array of functions - using this reference

Question

I'm trying to create a interface that defines the a interface with a array of functions and a this guard as below:

interface MyInterface {
  myFunctions: ((this:MyInterface, somevar: string): void)[];
}

But , when i try to use it as below:

class Myclass implements MyInterface {
  myFunctions: ((this:Implementation, somevar: string): void)[];
  useFunction (): void {
    this.myFunctions[0](somevar);
  }
}

The erro below happens Class 'Myclass ' incorrectly implements interface 'MyInterface'

Somebody knows how i do implements that ??

Your class implementation is different from your interface, so that's not allowed. I'm also not sure how an interface can have a function that implements itself .... — Kokodoko
– Kokodoko, Commented Nov 7, 2017 at 14:11

artem · Accepted Answer · 2017-11-07 14:39:59Z

1

First of all, function type is declared with => , not :

interface MyInterface {
  myFunctions: ((this:MyInterface, somevar: string) => void)[];
}

Second, why do you have this:Implementation in the class, not this.MyClass or this.MyInterface as declared in the interface? It should be consistent - either this.Implementation in the both class and interface, or this.MyInterface in the interface and this.MyClass in the class.

Then, in javascript (and typescript), for calling a function and setting it's this context the function name must be followed immediately by (, for example this.useFunction().

You have this.myFunctions[0](somevar) which means that you are calling the first element of myFunctions as free function, without setting its this context. You need to set this explicitly using call() here:

interface MyInterface {
  myFunctions: ((this:MyInterface, somevar: string) => void)[];
}

class Myclass implements MyInterface {
    myFunctions: ((this: Myclass, somevar: string) => void)[] = [];


    useFunction(somevar: any): void {
        this.myFunctions[0].call(this, somevar);
    }

}

answered Nov 7, 2017 at 14:39

artem

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1 Comment

Leonardocregis Over a year ago

Thanks for the help, the first error about how the function is declared was just my bad, it was like you said in the original source.

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