how-to-type-a-function-in-an-interface.md

How to Type a Function in an Interface

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In TypeScript you can type a function in two ways.

interface Bird {
  flapWings(flaps: number): number;
  sing: (song: string) => string;
}

let bird: Bird = {
  flapWings: function (flaps: number) {
    return flaps * 2
  },
  sing: (song: string) => `Chirp ${song} Chirp!`
}

example link