React Hooks for beginners
What are Hooks?
Once upon a time, before Hooks, if you had a function that you needed to add a state to, you had to convert the function to a class(to use State and setState()) and this needed to be defined in the constructor.
Hooks let you use state and other React features to achieve the same result in a functional component, without writing a class.
Some benefits are that writing functions instead of classes can have a great impact on performance and readability of the code. Plus, you don't need to reference the ‘this’ key word all over the place.
React hook rules
- You can only call hooks at the top level: This means that you can not call Hooks within loops, conditionals and nested functions.
- You should call them at the top of your react function. This is important because it allows React to call it in the same order every render.
How to use react hooks
The following will demonstrate the difference in code with hooks in a class component and a functional component. The hook useState() is the most used state, this is because any data that changes in the app is called state and when the state changes we want react to update the UI, so that the changes are reflected to the end user
useState(): A typical class component would use State as follows.
The state is defined within the constructor and set a default value of ‘count’ to 0. This code snippet shows that every time we click on the button, we add 1 to the value ‘count’.
The same thing can be achieved with a functional component :
You can already see that the code is much more condensed and is easier to read.
The main differences are:
- useState() is imported from React (line 1)
- The hook is called at the top of the function.
- The hook takes one optional argument, which is the default state, which has been set to ‘0’. Unlike classes, the ‘state’ here doesn’t have to be an object. We can call as many useState as we like.
- The function then returns an array that contains two values you can use within your component:
const [count, setCount] = useState(0)
- One more difference is that the class uses this.setState and then this.state.count when we can to access the value, where as in the functional component we can set up a new value using the function setCount and add 1 to the current count value (line 9).
Hooks are the new way to keep dynamic states in function components. We can use function components with hooks the same way that we write class components.
They coexist with existing class components and they’ll still be supported in the foreseeable future.