React Hooks
useState, useEffect, useContext, useRef, useCallback, useMemo, custom hooks
1Which function allows declaring a state variable in a React functional component?
Which function allows declaring a state variable in a React functional component?
Відповідь
useState is the fundamental hook for managing local state in functional components. It returns an array containing the current state value and a function to update it. Unlike class components that use this.state, functional components use useState for each independent state variable.
2What is the correct syntax to use useState with an initial value of 0?
What is the correct syntax to use useState with an initial value of 0?
Відповідь
The useState syntax uses array destructuring. The first element is the current state value, the second is the setter function to update it. The naming convention is to prefix the setter with 'set' followed by the capitalized variable name, like setCount for the count variable.
3When does the useEffect callback without a dependency array execute?
When does the useEffect callback without a dependency array execute?
Відповідь
Without a dependency array, useEffect runs after every render of the component, including the first render and all subsequent re-renders. This can cause performance issues as the code runs on every update. To limit executions, provide a dependency array specifying which values to watch.
How to run a useEffect only on component mount?
What is the purpose of the function returned by a useEffect?
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