Welcome to our exhaustive React Hooks guide. Follow along and fork my code at any point as we learn about everything from the basics all the way to advanced hooks usage examples such as useReducer for managing a list of data. This guide also provides background on the history of React and its concept of state management. Join me as we explore the ins and outs of React Hooks! Released in minor alpha Not believing in large rewrites that break backward compatibility, a gradual migration and adoption strategy allows the new API and patterns to co-exist with the older ones.
Hooks are an additive change to the core library. Meaning they are opt-in and backward compatible. If you want to use them, simply install the latest version of React.
The Hook pattern provides an alternative to writing class-based components and a simple to use state and has an alternative for lifecycle methods. Hooks bring to functional components the things we once were only able to do with classes, like being able to work with React local stateeffects and context through useStateuseEffect and useContext.
The easiest way to describe Hooks is to show side-by-side examples of a class component that needs to have access to state and lifecycle methods, and another example where we achieve the same thing with a functional component.
Below I provide a working example similar to those in the ReactJS docs, but one that you can touch and play around with, getting your hands dirty with a StackBlitz demo for each stage of our learning.
So let's stop talking and start learning about React Hooks. Hooks have a lot of benefit to us as developers, and they are going to change the way we write components for the better. They already help us to write clearer and more concise code - it's like we went on a code diet and we lost a lot of weight and we look better and feel better.
It brings out our jawline and makes us feel lighter on our toes. It's the one change that works for us. Just look at what React Hooks have done for others! All kidding aside, Hooks do trim the fat.
It cuts down and makes our code more readable, concise and clear. The side-by-side below shows how the component has lost a little weight. We not only save about five lines of code but the readability and test-ability also improve with the change over to Hooks.
Switching existing code over to Hooks could have a big impact on the sheer volume of code and readability, but I would encourage you to take it slow. Remember that Hooks is backward compatible with the code it's replacing and can live side by side with it, so there's no need to rewrite the whole codebase immediately. Check out the StackBlitz demos for this code: Before and After. If you would like, you can enforce these rules in your team with an ES Lint plugin.
Also on that same page there are good explanations on why these rules are required. Below we follow the canonical counter component example provided in the React documentation. It's a pretty simple demo that contains a button inside of a Counter component. Once clicked, it advances the state by one and updates the state.
The first thing to notice about the class-based component is that the class syntax uses a constructor, that references the this keyword. Inside the constructor, we have a state property. We also update the count using setState. In the functional component example, we have an additional import of useState.
There's no more class syntax or constructor, just a const. Its assignment sets the default and provides not only the count property but a function for modifying that state called setCount. This setCount refers to a function and can be named whatever you like.
I'm following this tutorialexcept Typescript cut my hopes short. See below. The App.
When the user logs in at the Login Component, my question is, how do I, via the AuthContextupdate the values in the App. If you take a look at the docs about React. The defaultValue argument is only used when a component does not have a matching Provider above it in the tree.
This can be helpful for testing components in isolation without wrapping them. Note: passing undefined as a Provider value does not cause consuming components to use defaultValue. So you don't need to pass anything to the context, but you are getting the error because of typescript.
This is how useContext works. Provider by value prop. How are we doing? Please help us improve Stack Overflow. Take our short survey. Learn more. Asked 2 months ago. Active 2 months ago.
Viewed times. I'm using Typescript. I want to Create a context Use the context in routing Update the context when logged in.
Hooks API Reference
See below I have this in my App. How do I update the context after login? KhoPhi KhoPhi 5, 6 6 gold badges 54 54 silver badges 98 98 bronze badges. Active Oldest Votes. You need to create an interface for the context value. Where is the "dispatch" magically coming from? Vencovsky Vencovsky 9, 1 1 gold badge 16 16 silver badges 44 44 bronze badges.
I appreciate the assistance. Unfortunately, still not clear to me, how to update the context from the login component. That useContext link in React docs, I've read it a million times. It doesn't make any sense to me. KhoPhi Please be more clear on how to update the context from the login component.
What you want to update? What you want to do? This isn't clear for me.Learn Development at Frontend Masters. It accepts a reducer function with the application initial state, returns the current application state, then dispatches a function.
Well, think about any situation where having the first loaded state of the application might be nice. The first and most important thing to understand about a reducer is that it will always only return one value. The job of a reducer is to reduce. That one value can be a number, a string, an array or an object, but it will always only be one. So, if we have an array of numbers, reduce will distill it down to a single number that adds up for as many times as there are values.
Say we have this simple array:. This will help us see how reduce distills the array into a single number. As we saw earlier, reduce takes dispatches a function that runs against a default state. See how reduce takes an initial value and builds on it as each number in the array is added to it until we get a final value? In this case, that final value is 6. I also really like this modified example from Dave Ceddia that shows how reduce can be used on an array of letters to spell a word:.
The classic example of this a counter application. In this example, we are making the assumption that the user has selected a car to purchase.
However, we want the app to allow the user to add extra options to the car. Each option has a price that adds to the base total.React Hooks useReducer Tutorial
When the user selects the item she wants, we update the features for the car, increase the additionalPrice and also remove the item from the store. We ensure that the other parts of the state remain as they are.
We do something similar when a user removes an item from the features list — reduce the additional price, return the item to the store. Here is how the App component looks like. The actions that get dispatched contains the details of the selected item. We make use of the action type to determine how the reducer function will handle the updating of the state. You can see that the rendered view changes based on what you do — buying an item from the store removes the item from the store and adds it to the list of features.
Also, the total amount gets updated. No doubt, there are some improvements that can be done to the application, this is only for learning purpose. An astute reader may have been asking this all along. I mean, setState is generally the same thingright? Return a stateful value and a function to re-render a component with that new value. We could have even used the useState hook in the counter example provided by the React docs. However, useReducer is preferred in cases where state has to go through complicated transitions.
If you take a look at the docs about React. The defaultValue argument is only used when a component does not have a matching Provider above it in the tree.
This can be helpful for testing components in isolation without wrapping them. Note: passing undefined as a Provider value does not cause consuming components to use defaultValue. So you don't need to pass anything to the context, but you are getting the error because of typescript. This is how useContext works. Provider by value prop. Learn more. Asked 2 months ago.
Active 2 months ago. Viewed times. I'm using Typescript. I want to Create a context Use the context in routing Update the context when logged in. See below I have this in my App. How do I update the context after login? KhoPhi KhoPhi 5, 6 6 gold badges 54 54 silver badges 98 98 bronze badges.
Active Oldest Votes. You need to create an interface for the context value. Where is the "dispatch" magically coming from? Vencovsky Vencovsky 9, 1 1 gold badge 16 16 silver badges 44 44 bronze badges. I appreciate the assistance. Unfortunately, still not clear to me, how to update the context from the login component. That useContext link in React docs, I've read it a million times.Will Redux get the hook?
For instance, if you have an array of numbers and you want to get the sum, you can write a reducer function and pass it to reducelike this:. What this does is call the function for each element of the array, passing in the previous total and the current element number. Whatever you return becomes the new total.
The second argument to reduce 0 in this case is the initial value for total. In this example, the function provided to reduce a. You pass a reducer function and an initial value initial state. Your reducer receives the current state and an actionand returns the new state. We could write one that works just like the summation reducer:. So… what triggers this? How does the action get in there? Good question. The first is the current state, and the second is a dispatch function. It could be a number, or an array, or anything else.
You can see how clicking the button dispatches an action with a value of 1, which gets added to the current state, and then the component re-renders with the new larger! Then create a component that sets up a ref and a reducer.
The ref will hold a reference to a form input, so that we can extract its value. We could also manage the input with state, passing the value and onChange props as usual, but this is a good chance to show off the useRef hook! The useRef hook allows you to create a persistent ref to a DOM node. Calling useRef creates an empty one or you can initialize it to a value by passing an argument.
The object returned by useRef is more than just a way to hold a DOM reference, though. It can hold any value specific to this component instance, and it persists between renders. Sound familiar? It should! The official Hooks FAQ has an example of using a ref as an instance variable.
Now need to write the handleSubmit function that will add an item to the list, as well as handle the action in the reducer.
The handleSubmit function is called when the user presses Enter in the input box, and so we need to call preventDefault to avoid a full page reload when that happens. Then it calls dispatch with an action.
Try the project at this stage in this CodeSandbox. Did you scroll down hoping to just read the answer? I guarantee this Hooks stuff will seem a lot less magical once you try it out a bit on your own, so I urge you to give it a try!
You can pretty safely argue that Redux is used in plenty of places where it is overkill including almost every example that teaches how to use it, mine included!
Redux provides a global store where you can keep app data centralized. Nothing would stop you from building your own mini-Redux with useReducer and useContextthough! And if you want to do that, and it fits your needs, go for it!GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. If nothing happens, download GitHub Desktop and try again. If nothing happens, download Xcode and try again. If nothing happens, download the GitHub extension for Visual Studio and try again.
A small project to help us understand the useReducer hook. We are replacing the code in our useEffect example with useReducer for state management. One quick note about cloning this project. If you wish to make commits and push the code up after cloning this repo, you should fork the project first. In order to own your own copy of this repository, you have to fork it so you get your own copy on your own profile! You can see the fork button in the top right corner of every GitHub project; click it and a copy of the project will be added to your GitHub profile under the same name as the original project.
After forking the project, simply clone it the way you would from the new forked project in your own GitHub repository and you can commit and push to it freely! In your terminal after you clone your project down, remember to run either yarn or npm install to build all the dependencies in the project.
How to Use the useReducer Hook
Find file. Sign in Sign up. Go back. Launching Xcode If nothing happens, download Xcode and try again. Latest commit. Latest commit 1cf Jul 1, How to fork and clone One quick note about cloning this project. After you fork and clone: Install dependencies In your terminal after you clone your project down, remember to run either yarn or npm install to build all the dependencies in the project. You signed in with another tab or window. Reload to refresh your session.If you haven't used state management excessively in React Function Componentsthis tutorial may help you to get a better understanding of how React Hooks -- such as useState, useReducer, and useContext -- can be used in combination for impressive state management in React applications.
In order to add a new todo item to our list of todo items, we need an input field to give a new todo item a potential task property. The id and complete properties will be automatically added to the item. In React, we can use the State Hook called useState to manage something like the value of an input field as state within the component:.
We also had to give our Function Arrow Component a body with an explicit return statement to get the useState hook in between.
How to Use the useReducer Hook
Now, we can change the task state with our handler function, because we have the input's value at our disposal in React's synthetic event:. Now the input field has become a controlled input fieldbecause the value comes directly from the React managed state and the handler changes the state. We implemented our first managed state with the State Hook in React.
The whole source code can be seen here. To continue, let's implement a submit button to add the new todo item to the list of items eventually:. The submit handler doesn't add the new todo item yet, but it makes the input field's value empty again after submitting the new todo item. Also it prevents the default behavior of the browser, because otherwise the browser would perform a refresh after the submit button has been clicked. In order to add the todo item to our list of todo items, we need to make the todo items managed as state within the component as well.
We can use again the useState hook:. By having the setTodos function at our disposal, we can add the new todo item to the list. The built-in array concat method can be used for this kind of scenario. Also the shorthand property name is used to allocate the task property in the object:.
There is one flaw in this implementation.