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Amateur blogger
Amateur blogger

Posted on • Updated on

useContext() with Typescript

The below article will give you an overview with an example of how to use the useContext() hook and also update the globally set context value in child components.

Prerequisites: Basic familiarity with React and Typescript

Usually, in a React application, data is passed top-down (parent to child) via props. The reason third party state management libraries like Redux became so popular is due to the prop drilling problem of React.

Prop drilling consists of passing a prop to the nested child components, and as a result, children who do not need this prop, still end up getting it even though they might never use it.

useContext() hook makes it easy to pass data throughout your app without manually passing props down the tree. It allows to create a global state and the required child components can consume it.

useContext() can prove to be a simple alternative to other state management libraries if your data is not complicated and the application is small.

This is what the process involves:

  1. Create a context object by using React.createContext()
  2. Provide the globally created context to your child >components using Provider

Example using Typescript:

In the below example, I want to set the value of content globally based on the user type passed which can be consumed by the nested child components. I will also update the value of content in one of the nested child component.

Let’s get started 🙌

  • Initialise, the context at a top-level using a default value. Create a global context hook useGlobalContext()

I have created a GlobalContent type which has copy and a setCopy(). The reason for using setCopy() will be clarified later.

import { createContext, useContext } from "react"
export type GlobalContent = {
  copy: string
  setCopy:(c: string) => void
}
export const MyGlobalContext = createContext<GlobalContent>({
copy: 'Hello World', // set a default value
setCopy: () => {},
})
export const useGlobalContext = () => useContext(MyGlobalContext)
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  • Wrap the context at the parent level to which the value of context would be accessible for its child components. I have wrapped it around the child components in App.tsx

In the below example, the getCopy() is getting the copy based on the logged in Admin user and making it available for the child components Home and About

import { MyGlobalContext } from './MyGlobalContext'
import React, { useState } from 'react'
import { getCopy } from './Content'
import { Home } from './Home'
import { About } from './About'
function App() {
const [copy, setCopy] = useState<string>(getCopy('Admin'))
return 
  (
   <MyGlobalContext.Provider value= {{ copy, setCopy }}>
     <Home/> 
    <About/>
  </MyGlobalContext.Provider>
  )
}
export default App
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  • Utilise the globally set value of copy in your child component Home.tsx
import { useGlobalContext } from './MyGlobalContext'
const Home = () => {
const { copy } = useGlobalContext()
return <div>{copy}</div>
}
export default Home
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That is it!!!! Your useContext() hook is in use and you have successfully set the value of copy i.e. content globally 😄.

You must be wondering why do we still have an unused setCopy() 🤔

As I mentioned at the beginning of the article, if you ever want to update the value of copy in child components, you need to pass a function to update the copy. In our case, setCopy() will allow you to update the copy.

In the below example, I am setting a new value for copy on the click of a button and passing it to the nested child component MyProfile.tsx

import { useGlobalContext } from './MyGlobalContext'
import { MyProfile } from './MyProfile'
const About = () => {
const { copy, setCopy } = useGlobalContext()
return(
   <>
    <button onClick={() => setCopy('This is a new copy')}>
      Click me!
    </button>
    <MyProfile newContent={copy} />
  </>
 )
}
export default About
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That’s it. Believe it or not, with what you learned above (or parts of it, really), you can start using useContext() hook and create a global state for your application.

Discussion (10)

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jedijetskyjodajedoindajaus profile image
jedidiah

It doesn't work for me, i don't have a getCopy, what this function does? could you please help me or get it touch with me!

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madv profile image
Amateur blogger Author

Hey! Thank you for your message and sorry for the inconvenience caused.
Basically, getCopy() method could be anything whose result you want to set globally. In my case, it is a simple method which gets content based on the logged in user type.
For eg:

const getCopy = (userType: string):string => 
{
   if (userType.toLowerCase() === 'admin')
   {
      return 'Hello Admin User!'
   }
   return 'Welcome user!'
}
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enough7 profile image
Enough7 • Edited on

You can use localstorage for this:

const USER_ID_KEY: string = "userId";
export let thisUser: IUser = {
    id: parseInt(localStorage.getItem(USER_ID_KEY) || '-1') 
};
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madv profile image
Amateur blogger Author

Thank you for the alternative, however what if the user has disabled his localStorage? ;)

Thread Thread
enough7 profile image
Enough7

I did not know you can disable it

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ofergal profile image
Ofer Gal

How will you change this when the objects to set and get are much more complex?
I have something like :
export interface IDocumentInfo {
file: IFilePickerResult;
pages?: number;
instructions?: string;
existsOnsite?: boolean;
}
export interface IRequestInfo {
projectNumber: string;
documents: IDocumentInfo[];
}

and I want a global context for an IRequestInfo object.
Thank you

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ben profile image
Ben Halpern

Nice post

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madv profile image
Amateur blogger Author

Thanks a lot Ben :). Being my first technical post, I am glad you liked it :)

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koaladlt profile image
Manuel de la Torre

Thanks a lot! I started lo learn Typescript recently and you save me a lot of time. I would buy you a beer if I could. Cheers!

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madv profile image
Amateur blogger Author

haha, that is really sweet Manuel! Glad, I was able to help :)