Plus, you can unit test the reducer even without a component! Let’s see how a stale state manifests itself. Consider a scenario when you’d like to count how many times a component renders. But how do you update it? Before React 16.7, if you are using functional components in your app then suddenly you have a requirement to add a bunch of state to your function; you have only one solution which is to convert your function to a class that extends React.Component then you'll use this.state to add initial state and setState() to update it. On later renderings of the component, getInitialState() is not invoked, skipping the expensive operation. The useState hook returns an array with 2 elements. How to zoom-in and zoom-out image using ReactJS? A stateless functional component doesn’t have a state. The returned array has 2 items: the current state and state updater function. This allows the component to use the componentDidMount life-cycle event and this.refs for accessing the form fields. As you know already, useState(initialState) returns an array where the first item is the state value. I create a functional component and in this component, I am using the useState hook, the second useState([data,updateData]) hook contains an array of objects and I … Using a wrapper function inside the React Hooks setter function is a better solution than the implementation just using .concat() or …. Mutable reference useRef() holds mutable data that, when changed, doesn’t trigger re-rendering. How to add Statefull component without constructor class in React? Adding a New Element to the State Array. Now since the state is an array, … The useState hook returns an array with 2 elements. Such events are a button click, an HTTP request completion, etc. This is why the React state itself (the searches variable and setSearches hook) were defined as constants using const — as a reminder of that. Let’s make these change to component: useState() is called at the first line of Bulbs function (don’t think about hook’s parameters and returned value for now). Wrapping the .push() in the setter function from React Hooks does not work either, even though it sort of seems like it should. . Reflected into state it should be initialized with false: useState(false) initializes the state with false. * @version 16.8.0 Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below. // changes state to `newState` and triggers re-rendering, // after re-render `state` has the value of `newState`, // after re-render `state` becomes `newState`, // Use dispatch({ type: 'add', item: movie }). We destructure the return value of the useState() hook to get a variable that contains the state array and a method for updating the state. After the state updater is called, React makes sure to re-render the component so that the new state becomes actual. Functional components are some of the more commonly used components in ReactJS. You can't update the array directly without using the method returned from useState().