> For the complete documentation index, see [llms.txt](https://shopify-1.gitbook.io/typescript/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://shopify-1.gitbook.io/typescript/beginner/functions/functions-as-types.md).

# Functions as types

As those familiar with JavaScript will know, functions themselves are values, and therefore, they have a type.

Let's take two functions, `multiply` and `echoString` as examples:

```typescript
function multiply(x: number, y: number): number {
  return x * y;
}

function echoString(input: string): string {
  return input;
}
```

We then declare our function type definitions using the following syntax:

```typescript
let myMultiply: (val1: number, val2: number) => number;
let myEchoString: (val: string) => string;

// Sanity check
myEchoString = echoString; // OK
myMultiply = echoString; // Error: type '(input: string) => string' is not assignable to type '(val1: number, val2: number) => number'
```


---

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