This is the second part of the series in learning React Hooks and the Context API. In the first part we learn the basics of useState, built the first parts of the Recipe Search application. The full code can be found on github
Overview of what we'll learn in this section
In this section, we'll work a little bit more with states just to completely understand the concept. We'll explain useEffect. Build the RecipeSearch component. We'll then refactor our state management strategy to make use of the Context API(useContext). Exciting right?
First things ...
We won't be making too many comparisons with classical components from here forward. Instead, we'll focus more on learning the fundamentals of hooks. From the last part, I have extracted the RecipeDetails into its own component. This is for two reasons
- It is the right thing to do, it's the point of component-based frameworks. It allows for code re-use.
- Also, this will give us ample opportunity to see the problem that arises with passing props around(
props drilling). And how context API can help us. More on that later! First, let's take a stab atuseEffect
A quick primer of the useEffect hook
In the first part, we mentioned and used the useEffect hook but didn't give any detailed explanations. I am certain only a few of us realize the problem with the way we have utilized the useEffect hook in the first part.
Hint: remember how we had to create our own separate JSON response. So as not to make too many API calls?.
Ha-ha, we are doing something terribly wrong just using useEffect as we did before. I will dive into that in a bit.
But first, what is this useEffect hook ?. As the name implies, it must have something to do with effects right?, if that's what you guessed you are absolutely correct. But what sort of effects?.
From official React documentation, effects are actions related to data fetching, setting up a subscription, and manually changing the DOM in React components. These are all examples of side effects. Some call it "side effects" others just call it 'effects". We are referring to the same thing.If you’re familiar with React class lifecycle methods, you can think of useEffect Hook as componentDidMount, componentDidUpdate, and componentWillUnmount combined.
Using the useEffect hook correctly.
Let's relate this information to our application. In App.js we have fetched data from the food2fork API function and then called the function in the useEffect function. This is equivalent to calling it inside the componentDidMount function. Let's take a closer look.
But think about it for a second. What is the intended use of componentDidMount?, the answer is in the name!. You only ever want to run any function inside this function when the component is mounted. Let's go over that information slowly. Mounting - is phase the component is created (your code, and react’s internals) then inserted into the DOM.
But, if you have a function that causes a repeated effect inside a componentDidMount your component will continuously re-render except you find a way to clean it up. This is done usually within the componentWillUnmount lifecycle.
How then does useEffect manage to replace componentDidMount and componentWillUnmount within one function. Let's revisit our wrong use of the useEffect to have a better grab of this. When we call the useEffect like below, the components continuously re-renders because it has no clue how to unmount. This is a terrible performance bottleneck.
// this isn't quite right. It works, but we'll see the problem later on
useEffect(() => {
fetchRecipe()
})
Let's do a post morterm to see the problem in action. Inside the fetchRecipe() in the App.js, try console logging something to indicate when the component is rendered. We could have also just inspected the Network tab in the browser. But sometimes console logging and seeing it in action will probably drive the point home faster.
On the third/hook-in-app.js branch of the repo. Edit App.js add the console.log and pop open your console. You should have something similar to below in the App.js for this little experiment.
import React, { useState, useEffect } from 'react';
import RecipeList from './components/RecipeList'
import RecipeDetails from './components/RecipeDetails'
function App() {
const apiKey = `36920f6651c9cd9d91a6c3205cabaa19`
let url = `https://www.food2fork.com/api/search?key=${apiKey}`
const [showHomeButton, setShowHomeButton] = useState(false)
const [recipes, setRecipes] = useState([])
const [loading, setLoading] = useState(true)
const [search, setSearch] = useState('')
const fetchRecipe = async () => {
const recipeData = await fetch(url)
const { recipes } = await recipeData.json()
setRecipes(recipes)
setLoading(false)
console.log("I am beign rendered again and again")
}
useEffect(() => {
fetchRecipe()
})
return (
<div>
{loading ? <h1 className="text-center">...fetching {search} Recipe</h1> :
<RecipeList recipes={recipes} />}
</div>
);
}
You will get the horror below. What the hell is happening? This is not even acceptable behavior. We got away with it because of the JSON response I created. We could make unlimited API calls without issues. Obviously, this cannot be the right way to do things in production. So what's the problem? or even the solution.
What is immediately clear is that the fetchRecipe continuously tries to fetch a response from the API and is being re-rendered every time by useEffect. Even though nothing has changed. We naturally would have had to clean this up in a class component by unsubscribing from the API call within another componentWillUnmount. Let's look at how useEffect handle this problem.
Now that we have appreciated the problem, let's think about the solution. Pause for a moment, what do we actually intend to achieve? In our case we want the fetchRecipe function to run only once when the component mounts - that is fetch data once and display it. Or when anything has an effect on the result of the function. At this point, nothing affects the result. So how do we then overcome this problem? Quite simple it turns out.
Inside the useEffect function, we simply pass an empty array as the second parameter. Hence, we are indicating to the useEffect not to update except when the component is first mounted since we expect nothing to cause fetch recipe function to update. Just like below.
useEffect(() => {
fetchRecipe()
}, []) // pass an empty array here.
And now if you went back into the App.js and do a console.log, you will realize fetchRecipe only runs once.
This is great, works well for our case. But what if we wanted to update and re-render after something causes fetchRecipe to change. You might ask what could this be. Let's say we have a state that changes the url for fetching the data. It means the data from fetchRecipe depends on url. We just simply pass that parameter inside the array passed to useEffect. Hence, we can pass as many parameters as needed into the array.
useEffect(() => {
fetchRecipe()
}, [url,query])
What you are saying in human language to
useEffectis that: only update whenurlorqueryparameter changes.
I recommend RobinWieruch tutorial for more examples if you still get confused.
Getting back to our app...
Let's build the RecipeSearch component.
Armed with the knowledge of safely fetching data, we'll now switch to using the API key from food2fork. Hence, we'll be doing some refactoring within App.js. We'll also introduce the best practice of having a try catch block inside the async function to catch any errors.
clone the
4/feature/implemented-searchbranch of the repo to follow along.
First, let's think of what we want to achieve with the search component and then think of how to achieve this. So, we want to enter a search, when we click submit or press enter, we want to change the content of the page to the new search result. And we also would want to be able to go back to the top 30 recipes, and thus clearing the search (or return to the top 30 results, depending on how you think about it). See what I mean below.
Now, we have a goal in mind, how do we write the code with hooks. Note, I am trying to make this as basic as possible, such that even with very basic React knowledge you can still build this. So not everything is exactly hook specific.
Immediately, it becomes obvious we definitely need some states to manage all those changes. First, we fetch another set of 30 recipe related to our search query. That's one state. We also have to decide when the Go back Home button should appear or disappear, you got it mate!. That's another state. Lastly, and perhaps the most important state is that holding our search parameter.
Like previously, let's look at how the code looks like in the App.js and then explain it line by line. Full code for search feature here
import React, { useState, useEffect } from 'react';
import RecipeList from './components/RecipeList';
import './App.css'
function App() {
// remeber to replace key
const apiKey = `36920f6651c9cd9d91a6c3205cabaa19`
let url = `https://www.food2fork.com/api/search?key=${apiKey}`
const [showHomeButton, setShowHomeButton] = useState(false)
const [recipes, setRecipes] = useState([])
const [loading, setLoading] = useState(true)
const [search, setSearch] = useState('')
const [error, setError] = useState('')
const fetchRecipe = async () => {
try {
const recipeData = await fetch(url)
const { recipes } = await recipeData.json()
setRecipes(recipes)
setLoading(false)
} catch (e) {
if (e) {
setError(e.message)
console.log(error)
}
}
}
const handleSubmit = async (e) => {
e.preventDefault()
try {
setLoading(true)
const searchUrl = `${url}&q=${search}`
const searchedRecipeData = await fetch(searchUrl)
const { recipes } = await searchedRecipeData.json()
setRecipes(recipes)
setLoading(false)
setShowHomeButton(true)
} catch (e) {
console.log(e)
}
}
const handleSearchChange = (e) => {
setSearch(e.target.value)
}
const handleReturnHome = () => {
fetchRecipe()
setShowHomeButton(false)
}
useEffect(() => {
fetchRecipe()
}, [])
return (
<div>
{loading ? <h1 className="text-center">...fetching {search} Recipe</h1> :
<RecipeList
search={search}
handleSubmit={handleSubmit}
handleSearchChange={handleSearchChange}
recipes={recipes}
showHomeButton={showHomeButton}
handleReturnHome={handleReturnHome} />}
</div>
);
}
export default App;
Noticed, how we have changed a couple of things. First, we are now safely making API requests directly. Hence, we are using our real API keys. It will become apparent why we can't continue using my json anyways. Let's go line, by line.
We have set a variable for the url. We know how the URL endpoint looks like from the food2fork documentation. Next, we set up a state with for showHomeButton to handle visibility for the home button. And set the initial value to false. That is,
initially when we'll be in the home page, there's no point displaying home button. The next two states are already familiar. Then we have the search state, and we set the original value to an empty string. Since we are not searching for anything yet when we first visit the home page.
Next, we have to manage how we respond to user typing in the search query. We have set up the handleSearchChange function to handle that. We have the handleSubmit button to take care of updating the data in the list to match the result from the search. And finally, we have the handleReturnHome function to obviously, you guessed right. Help us return home safely with just the 30 top recipes.
Let's examine how each function performs its duty.
First, handleSearchChange . The purpose is to capture user entry and then update the search state to equal user entry. This is quite straight forward as the function body is even just 1 line.
const handleSearchChange = (event) => {
setSearch(event.target.value)
}
Here is how it works, since we are responding to user input, we have access to the onChange property from the event object. We have simply grabbed the value from the event.target.value and updated the search state with this value using the setSearch hook. We then need to pass them as props all the way down to the RecipeSearch component like below. This is one of those things to solve with Context API.
Next, let's examine the most interesting function in App.js. The handleSubmit. What does it do? Let's look at the code first and then explain.
const handleSubmit = async (e) => {
e.preventDefault()
try {
setLoading(true)
const searchUrl = `${url}&q=${search}`
const searchedRecipeData = await fetch(searchUrl)
const { recipes } = await searchedRecipeData.json()
setRecipes(recipes)
setLoading(false)
setShowHomeButton(true)
} catch (e) {
console.log(e)
}
}
Since this is going to be triggered on submit. We have access to the event object. First, we need to prevent the default behavior of onSubmit which is to reload the page, hence we have e.preventDefault(). We set the loading state to true with setLoading(true) indicating we are still fetching data. We then take the current state of search that is now equal to the input by the user. We use this to create a new API point based on the documentation we have from food2fork. And then fetches new data based on this search query. It then updates the current recipe state with setRecipe to match with the new data from the search query. Now that we have the data we set loading state to false using setLoading(false). Now the new recipe list is based on the search query, we need a way to go back home. Hence, we have set the showHomeButton to true using setShowHomeButton.
Lastly, we have the handleReturnHome function whose job is to get us back home with the top 30 recipe list. So we simply fetched recipe as we did originally, this already sets back the recipe state back to how it was. We then set the showHomeButton back to false, making the button disappear when we are on the home page. We then simply passed down all the required states as props to child components where we'd use them.
The Context API
React Context API is essentially a way to create global states that can be used anywhere within the application. This is an alternative to passing down props from grandparents to children and so on. It's been touted as a lighter alternative to Redux. In my experience, I will say it more closely resembles Vue's VueX. Where you have a single source of truth and can access that state globally.
Let's examine the case of props drilling in our application. You can imagine in an application simple as this, we already have to pass props from App.js through RecipeList and then to RecipeSearch. Even though RecipeList component does not need the handlesSubmit and handlesSearchChange props we still need to pass them through because it's the parent component to RecipeSearch. Imagine more deeply nested components trees, then you can already see chaos. Libraries like Redux helps solve this problem but context is a simple lightweight version.
useContext hook to the rescue
So what if we could access whatever state we want higher up within the component tree and just use them only where they are needed. This is what we are going to do next with useContext hook. There are a couple of things to understand with context API.
- Context is designed to share data that can be considered “global” for a tree of React components.
- Context is primarily used when some data needs to be accessible by many components at different nesting level
Let's discuss the API that context gives us. First we have React.createContext. It create a Context object. When React renders a component that subscribes to this Context object it will read the current context value from the closest matching Provider above it in the tree.
Context.Provider - Every Context object comes with a Provider React component that allows consuming components to subscribe to context changes.
Context.Consumer - A React component that subscribes to context changes. This lets you subscribe to a context within a function component.
Let's bundle all this into our example and see how it works.
First, let's create a context folder or just a file with and index.js file in it. Inside index.js we need to create a Provider that accepts and provides the data to all children components within it. First, let's move all our data fetching logic from App.js into the context file. You should be left with an almost empty App.js like below.
import React, { useContext } from 'react';
import RecipeList from './components/RecipeList'
function App() {
return (
<div>
{loading ? <h1 className="text-center">...fetching {search} recipe</h1> :
<RecipeList />}
</div>
);
}
export default App;
And index.js ...
import React, { useState, useEffect } from 'react'
const RecipeContext = React.createContext()
const apiKey = `7cdab426afc366070dab735500555521`
const RecipeProvider = (props) => {
let url = `https://www.food2fork.com/api/search?key=${apiKey}`
const [showHomeButton, setShowHomeButton] = useState(false)
const [recipes, setRecipes] = useState([])
const [loading, setLoading] = useState(true)
const [search, setSearch] = useState('')
const fetchRecipe = async () => {
try {
const recipeData = await fetch(url)
const { recipes } = await recipeData.json()
setRecipes(recipes)
setLoading(false)
console.log(recipes)
} catch (e) {
if (e) {
console.log(e.message, 'Try updating the API key in App.js')
}
}
}
const handleSubmit = async (e) => {
e.preventDefault()
try {
setLoading(true)
const searchUrl = `${url}&q=${search}`
const searchedRecipeData = await fetch(searchUrl)
const { recipes } = await searchedRecipeData.json()
setRecipes(recipes)
setLoading(false)
setShowHomeButton(true)
} catch (e) {
console.log(e)
}
}
const handleSearchChange = (e) => {
setSearch(e.target.value)
}
const handleReturnHome = () => {
fetchRecipe()
setShowHomeButton(false)
}
useEffect(() => {
fetchRecipe()
}, [])
return (
<RecipeContext.Provider value={{
loading,
search,
showHomeButton,
recipes,
handleSearchChange,
handleSubmit,
handleReturnHome,
}}>
{props.children}
</RecipeContext.Provider>
)
}
export { RecipeProvider, RecipeContext }
Let's try to understand the above code by taking it apart carefully.
We have simply moved all the logic for data fetching from our App.js into index.js so as to make it available globally. We already know the drill, we have the data and the states just like we did before.
Now, to the interesting part, on line 2. We have created the RecipeContext from React.createContext() method. RecipeContext is just a variable, the name is not relevant, it is simply good practice to give it a name close to what it does. When we created the RecipeContext it gives us access to 2 other properties namely the Provider and the Consumer. The Provider gives us a way to pass all the data and states as props from the topmost part of React tree to wherever we would like to consume it. Hence we created RecipeContext.Provider and passed down all states and data as a prop called *value *. We then export these values to be used. Like below. It will become clearer when we begin to use them.
<RecipeContext.Provider value={{
loading,
search,
showHomeButton,
recipes,
handleSearchChange,
handleSubmit,
handleReturnHome,
}}>
{props.children}
</RecipeContext.Provider>
)
}
export { RecipeProvider, RecipeContext }
Next, we have to locate the highest tree in our component hierarchy to pass the value props to. It's only through this way that it can be able to pass it along to all its children. And that would be the index.js in our root. This is where the App component is located. Hence, the App component is able to pass any data or state as props to wherever it will be needed. In the index,js in the root of your application. You should wrap the RecipeProvider around App like below.
import React from 'react';
import ReactDOM from 'react-dom';
import { RecipeProvider } from './context/index'
ReactDOM.render(
<RecipeProvider>
<App />
</RecipeProvider>
, document.getElementById('root'));
From here henceforth all the props pass down inside our context file is available to all the children of App component, which is essentially every component. The exciting part is how we'll then use this. We'll make an example with RecipeList and RecipeSearch components. Your RecipeList component should look like below.
import React, { useContext } from 'react'
import Recipe from './Recipe'
import RecipeSearch from './RecipeSearch'
import { RecipeContext } from '../context/index'
export default function RecipeList() {
const appContext = useContext(RecipeContext)
const { showHomeButton, recipes, handleReturnHome } = appContext
return (
<>
<RecipeSearch></RecipeSearch>
<div className="container my-5 home-button">
{showHomeButton && <button type="button"
className="btn btn-warning"
onClick={() => handleReturnHome()}>
Go Back Home
</button>}
<div className=" d-flex d-flex justify-content-center mb-3">
<h1 className="text-slaned ">Recipe List</h1>
</div>
<div className="row recipe-list">
{recipes.map(recipe => {
return <Recipe
key={recipe.recipe_id} recipe={recipe} />
})}
</div>
</div>
</>
)
}
We have now imported RecipeContext from our file and imported useContext from React. Inside our function, we created a variable to hold the value of RecipeContext. We then just grab only the values we need inside RecipeList. This is so clean in many ways, 2 of which are.
- First, we just went to
RecipeListstraight where we needed those states and data, we didn't have to thread the props from parent to children. - Second, we only extracted the props we needed within the component, we didn't need to give
RecipeListsome props it didn't need but just has to pass along to its children. We just go to that child component directly if they needed the data.
Let's examine RecipeSearch component. Once again, let's see the code and then explain it.
import React, { useContext } from 'react'
import { RecipeContext } from '../context/index'
export default function RecipeSearch() {
const appContext = useContext(RecipeContext)
const { handleSubmit, handleSearchChange } = appContext
return (
<div className="container d-flex justify-content-center my-5">
<form className="form-inline" onSubmit={(e) => handleSubmit(e)}>
<label htmlFor="search" >Search:</label>
<input data-age="Love" onChange={(e) => handleSearchChange(e)} type="text" className="form-control" id="search" placeholder="coffeee" name="search" />
<button type="submit" className="btn btn-primary"><i className="fa fa-search"></i></button>
</form>
</div>
)
}
Like in the RecipeList we have imported useContext and RecipeContext. We created the variables. And just see how clean and concise this is, we didn't have to get handleSubmit and handleSearchChange from RecipeList we just simply grabbed them from the context here.
And that's just about it. We have covered 3 major types of hooks. useState, useEffect and useContext. I believe these are the foundation necessary to understand more advanced and better ways to work with react hooks. I believe they are cleaner and easier to digest for a beginner.
Moving forward, if you'd like to gain a deeper understanding. You can refactor the Recipe component to use the useContext. Take an old project with a class component and convert it into a functional component just using hooks. If you want something more challenging, learn the useReducer hook and how we can refactor multiple states in our context file to make use of useReducer
Thank you!. The full code can be found on github. Comments and feedback are welcomed.
Top comments (9)
Hi Ola. That was a very comprehensive post. Thanks for taking out time for writing it. I cam creating an app as a side project. I got some nice ideas. The only difference is that I am using multiple recipe apis from this for recipes.
Hello Ola! I'm new to Web Development from Argentina, started this last January.
I'm not used to do this (leave a review), but just needed to let you know that this article was super usefull to me, and the way that you chose to teach, comparing different forms and correcting past mistakes was actually awesome. Of course that i'm gratefull to you, and will share it with friends so they might learn a lot of things the same way i did. Take care!
Thanks Ola,
Alan
So happy to hear, glad it was helpful. And hope you got it all working
I really appreciate this article. I'm currently working on an Anime database project and was trying to make it a little more clean and this solved one of my major issues. 🙏
That's great to hear. I am happy I could help. Let me know if you need additional support
Thanks for this article and the project code!
Ola this is epic
Great post! Very useful, thank you!