We're a place where coders share, stay up-to-date and grow their careers. But this version of is easier to understand, because the state management’s been extracted into the reducer.
Now you have the first grasp of how to use useState(). Let’s use array destructuring to extract the state value into a variable on: Ok, the state’s been enabled and initialized, and now you can read it. As Juan Gabriel S. Palarpalar mentioned in comments, there's no need to use refs in this case.

setState Callback in a Functional Component. When On button is clicked, lightOn() handler updates the state to true: setOn(true). The first React.useEffect hook has an empty array. We strive for transparency and don't collect excess data. Instead, we use the useEffect Hook and its second argument, which is an array of dependencies. It’s important that calling the hook inside the component makes it a stateful functional component.

To fix the problem of re-creating the toggle callback we need a way to avoid depending on isToggled directly but still have its actual value inside a callback. Call useState() hook to enable state in a functional component. It declares a “state variable”. This really makes the hook way clearer: At the end of the day, useCallback is only about optimization.
Sounds good. As soon as the state changes, React re-renders the component. If the initial state is a primitive value (number, boolean, etc) there are no performance issues. React makes sure the latest state value is supplied as an argument to the update state function. I'm excited to start my coaching program to help you advance your JavaScript knowledge. First, let's create a simple RendersCounter component that takes a single onClick prop. For complex state management, it’s reasonable to stick to useReducer() hook. To make sure the value in isToggledRef is up-to-date we use useEffect with a single isToggled dependency in the dependencies array. Every time React re-renders the component, useState(initialState) is executed. Now let's use this component to see what happens if we don't pass dependencies to useCallback at all. To perform side effects after state has change, you must use the React.useEffect hook. The second parameter this.setState() accepts is the callback function, and that’s where you’ll want to add your side effects. In the beginning, the bulb is switched off. Luckily, the second item is a function that updates the state! Our only question is, are you in. On multiple useState() calls, the invocation order must be the same between renderings. To do so, you need a functional component with state, aka stateful functional component. Click “Increase async” quickly a few times.

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