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Questions and Answers
What is the purpose of the useState Hook in React?
It lets us keep local state in a function component.
What is the value that the counter variable is initialized to?
Zero
What is the purpose of the second returned item from the useState Hook?
It lets us update the counter.
What is array destructuring in JavaScript?
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Can we name our own state variables in React?
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What is the syntax difference between React events and DOM events?
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How do we pass an event handler in JSX?
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What happens if we call useState multiple times in a component?
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What is the benefit of using multiple state variables?
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What is the purpose of the setCounter function?
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Study Notes
Fixing Common Mistakes with useEffect
- If you don't provide the dependencies array to useEffect, it will run after every render, leading to infinite loops when updating state.
- To fix this, provide an empty dependencies array to run the effect function only once after the component has rendered the first time.
Using useEffect with API Calls
- Here's an example of a simple React app that fetches users from JSONPlaceholder using the useEffect hook.
Introducing React Hooks
- Hooks are a new feature introduced in React 16.8 that allows using state and other React features without writing a class.
- Hooks are functions that "hook into" React state and lifecycle features from function components.
- Hooks do not work inside classes and are backward-compatible.
- Two rules to follow when using Hooks:
- Only call Hooks at the top level.
- Only call Hooks from React functions.
State in React
- In React, "state" refers to the data that represents the current condition of a component.
- State allows React components to create dynamic and interactive UIs.
Functional Components vs. Class Components
- There are two main types of components in React: functional components and class components.
- Functional components are simple JavaScript functions that take props as an argument and return JSX.
- Prior to React 16.8, functional components couldn't manage state, but with the introduction of Hooks, particularly useState, functional components can now manage state.
Implementation of useState Hook
- We import the useState Hook from React to keep local state in a function component.
- useState returns a pair of values: the current state value and a function to update it.
- We can declare multiple state variables using an array.
Counter App Example
- We create a React project that uses the useState hook to implement a counter application.
- We declare a new state variable by calling the useState Hook and initialize it to zero.
- We use the setCounter function to update the counter state.
What Do Square Brackets Mean?
- The square brackets in useState are part of JavaScript's array destructuring syntax.
- This syntax allows us to give different names to the state variables we declared.
Using Multiple State Variables
- We can declare multiple state variables using the array destructuring syntax.
- React assumes that if you call useState many times, you do it in the same order during every render.
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Description
Learn how to fix common mistakes when using the useEffect hook in React, including providing dependencies and handling state updates.
