I'm migrating a React with TypeScript project to use hooks features (React v16.7.0-alpha), but I cannot figure out how to set typings of the destructured elements.
Here is an example:
interface IUser {
name: string;
}
...
const [user, setUser] = useState({name: 'Jon'});
I want to force user variable to be of type IUser. My only successful trial, is doing it in two phases: Typing, then initializing:
let user: IUser;
let setUser: any;
[user, setUser] = useState({name: 'Jon'});
But I'm sure there is a better way. Also, setUser should be initialized as a function that takes a IUser as input, and returns nothing.
Also, worth noting that using const [user, setUser] = useState({name: 'Jon'}); without any initialization works fine, but I would like to take advantage of TypeScript to force type checking on init, especially if it depends on some props.
Thanks for your help.
Use this
const [user, setUser] = useState<IUser>({name: 'Jon'});
First useState takes a generic, which will be your IUser. If you then want to pass around the second destructured element that is returned by useState you will need to import Dispatch. Consider this extended version of your example that has a click handler:
import React, { useState, Dispatch } from 'react';
interface IUser {
name: string;
}
export const yourComponent = (setUser: Dispatch<IUser>) => {
const [user, setUser] = useState<IUser>({name: 'Jon'});
const clickHander = (stateSetter: Dispatch<IUser>) => {
stateSetter({name : 'Jane'});
}
return (
<div>
<button onClick={() => { clickHander(setUser) }}>Change Name</button>
</div>
)
}
See this answer.
You could also declare the initial state before and then be able to call it any time you want:
type User = typeof initUser;
const initUser = {name: 'Jon'}
...
const [user, setUser] = useState<User>(initUser);
About I interface prefixes: https://basarat.gitbooks.io/typescript/content/docs/styleguide/styleguide.html#interface