Hooks Rundown

React Hooks allow users to pass and access data within functional components in React. They allow users to access built-in React features such as state, context, and more. If you haven't yet encountered Hooks, read more about them here.

The Cheat Sheet

The point of this post isn't to teach you hooks; It's to give you an easy guide to refer to without digging through the docs because you forgot some simple syntax. I'll provide a more in-depth explanation of each hook below if you ever need a refresher.

import { useState, useEffect, useContext, useRef } from 'react'

useState : Access and modify internal state objects

const [name, setName] = useState("default_user")

• Takes one optional parameter that sets the default value of the state object
• Returns a reference to internal state object and a setter function for that state object
• Triggers a rerender of the whole component which is default behavior when state is changed

useEffect : Call a function whenever a component is rendered or a state dependency is changed

useEffect(callbackFunction, [dependencies])

• Takes 1 required parameter: a function and 1 optional parameter: an array of dependencies
  • [ ] - no dependencies, only runs on initial component render
  • [name] - runs when variable name is changed, including initial render
  • null - all states are dependencies, runs on initial render and every state change / rerender
• Calls given function whenever dependencies are changed

useContext : Access internal context props provided by parent

const user = React.useContext(MyContext)

• Takes one argument: the context object created with React.createContext()
• Returns whatever data was passed to the context provider value

1. Create context object

   const UserContext = React.createContext()
   

2. Create context provider

   function UserProvider({children}){
   
       const user = {
           name: "puppy_lover_2024",
           avatar: "pexels.com/photo/puppy/"
       }
   
       return(
           <UserContext.Provider value={user}>
               {children}
           </UserContext.Provider>
       )
   }
   

3. Wrap children components in context provider

   function App() {
       return (
           <UserProvider>
               [screenComponents]
           </UserProvider>
       )
   }
   

4. Access the context using the useContext in a child component

   const user = React.useContext(UserContext)

useRef - references in internal variable that persists across rerenders but does not trigger them

const numRenders = useRef(1)

• Takes one argument: a default value for the variable
• Returns a reference to that variable which has a property .current that can be treated like any prop/variable

• Useful for keeping track of previous state values and referencing DOM elements
  

  function ReferencedDiv({children}){
      const currentDiv = useRef()
      return(
          <div ref={currentDiv}>
              {children}
          </div>
      )
  }
  

import { useParams, useRouteError, useOutletContext, useNavigate } from 'react-router-DOM

useParams - access data stored in current URL

const params = useParams()

• Takes no arguments

• Returns object with a key of whate the router was told to expect and a value of the parameter that exists in the link itself

  • In Router:

  {
      path: "/profile/:name", element <ProfilePage/>
  }
  

  • In Link:

  <Link to={ `/profile/puppy_lover_2024` }>
      View Profile
  </Link>
  

  • Returned:

  return( useParams() )
  -> { name: "/profile/puppy_lover_2024" }
  

useNavigate - Returns function to programmatically navigate to given route

const navigate = useNavigate()

• Takes no arguments

• Returns a function that will navigate to given route param
  

  const navigate = useNavigate()
  
  ...
  
  navigate("/login")
  

useRouteError - catch any error in the UI and reroute to this component

const error = useRouteError()

• Takes no arguments
• Returns the error that caused the reroute to this page / component

useOutletContext - accesses data stored in the direct parent Outlet's context

const myData = useOutletContext()

• Takes no arguments

• Returns the object passed to context parameter in parent

  • In Outlet (parent component):

  <Outlet context={ name: "puppy_lover_2024" }>
  

  • Returned :

  return( useOutletContext() )
  
  -> { name: "/profile/puppy_lover_2024" }
  

• Only works if the Outlet is this components direct parent