interface.md

interface

Interface declaration

interface I {
    x: number;
    readonly z: string; // field with readonly modifier
    foo: () => number;  // method
    set m(v: number);   // setter
    get m();            // getter
}

Implement interface

class C implements I {
    x: number = 0;
    z: string = "z";
    get m() {
        return this.x;
    }
    set m(v: number) {
        this.x = v;
    }
    foo(): number {
        return 0;
    }
}

In TypeScript, implements is not required, any objects satisfies the fields defined by the interface are treated implemented those interfaces. But it is recommended to use implements when using ts2wasm-compiler since the compiler may apply further optimization according to these information.

Assign to interface

interface can be assigned from an object literal or class instance.

interface I {
    x: number;
}

let obj: I = {
    x: 10,
}

class A {
    y: number = 2;
    x: number = 1;
}

obj = new A();

Optional fields

interface I {
    x: number;
    y?: number;
}

let i : I = { x: 1 };

Reading an un-exist optional field will return undefined. Writing an un-exist optional field will cause an error since it's not possible to add a new field to an static object.

console.log(i.y);   // undefined
i.y = 1;            // runtime error

Limitations

• interface extends is not supported

  interface I1 {
      x: number;
  }
  
  // Not Supported
  interface I2 extends I1 {
      y: number;
  }

• indexed signature interface is not supported

  interface I {
      [index: number]: number;
  }

• function signature interface is not supported

  interface I {
      (x: number): number;
  }