Learn React with TypeScript 3

Generic functions

Let's go through an example of a generic function. We are going to create a wrapper function around the fetch JavaScript function for getting data from a web service:

1. Let's start by creating the function signature:

function getData<T>(url: string): Promise<T> {}

We place a T in angled brackets after the function name to denote that it is a generic function. We can actually use any letter, but T is commonly used. We then use T in the signature where the type is generic. In our example, the generic bit is the return type, so we are returning Promise<T>.

If we wanted to use an arrow function, this would be:

const getData = <T>(url: string): Promise<T> => {  };

2. Let's now implement our function:

function getData<T>(url: string): ...