# How to Type a Higher Order Function in Typescript

Given a higher order function like the following:

```
function higherOrderFunction(a:number, b: number) {
return (a: number): number => {
return a*b
}
}
```

This causes a problem when typing the function as typing in the usual way does not work.

We could type it as a `Function`

, this is valid, but ambiguous.

Extending `Function`

allows us to create a non-ambiguous type for the function

```
interface HigherOrderFunction extends Function {
(a:number): number
}
```

Our final result with typing:

```
interface HigherOrderFunction extends Function {
(a:number): number
}
function higherOrderFunction(b: number): HigherOrderFunction {
return (a: number): number => {
return a * b
};
}
```

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