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All 12 useState & useEffect Mistakes Junior React Developers Still Make in 2024

ByteGrad・55 minutes read

Always update state using the updater function to avoid issues with outdated values, utilize one object state for forms with specific property updates, manage complex state logic by breaking it down, and optimize performance by avoiding unnecessary re-renders. TypeScript helps infer variable types, ensures compatibility in operations, enforces type checking for data integrity, and allows custom types for complex structures to prevent errors and improve code quality.

Insights

  • Mistake #12: Duplicating state update lines doesn't increase count as expected; scheduling state updates causes the issue.
  • Solution: Use the updater function version of updating state to access the most up-to-date value.
  • Objects and arrays in JavaScript are passed by reference, leading to re-renders when updating an object due to React recognizing a change in the reference.
  • When setting state with an object, React may re-render due to the change in the object's reference, unlike with primitive values like numbers or strings.

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Recent questions

  • How can I update an object's state without losing properties?

    Spread existing object properties when updating.

  • How can I efficiently manage state for a form with multiple inputs?

    Use one object state for the entire form.

  • How can I dynamically update multiple properties in an object state?

    Utilize the event's target name attribute.

  • How can I calculate and update the total price based on quantity changes?

    Use a dependency array in a function to calculate the total price.

  • How can I optimize the use of useEffect to prevent unnecessary re-renders?

    Focus on essential updates and avoid excessive re-renders.

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Summary

00:00

Avoid common React state management mistakes

  • Mistake #12: Duplicating state update lines doesn't increase count as expected; scheduling state updates causes the issue.
  • Solution: Use the updater function version of updating state to access the most up-to-date value.
  • Mistake #11: Conditional rendering can cause issues with hooks if not handled correctly.
  • Solution: Ensure hooks are used consistently in every render to avoid errors.
  • Mistake #10: Incorrectly updating an object's state can lead to missing properties.
  • Solution: Spread the existing object properties when updating to retain all values.
  • Mistake #9: Using separate states for each form input can be inefficient.
  • Solution: Use one object state for the entire form and update specific properties using the spread operator.
  • Mistake #8: Updating multiple properties in an object state requires a dynamic approach.
  • Solution: Utilize the event's target name attribute to dynamically update object properties based on input names.
  • Mistake #7: Handling quantity and total price in a cart component can lead to state management issues.
  • Solution: Calculate the total price based on the quantity and update it accordingly.
  • Mistake #6: Managing complex state logic can become convoluted without proper structuring.
  • Solution: Organize state management by breaking down complex logic into smaller, manageable parts.
  • Mistake #5: Overusing useEffect can lead to unnecessary re-renders and performance issues.
  • Solution: Optimize the use of useEffect by focusing on essential updates and avoiding excessive re-renders.
  • Mistake #4: Not utilizing useMemo for expensive calculations can impact performance.
  • Solution: Use useMemo to cache and optimize expensive calculations for improved performance.

11:54

Automatic Total Price Update Based on Quantity

  • To update the total price based on quantity changes, use a dependency array in a function that calculates the total price as quantity times price per item.
  • By setting up the function to run every time the quantity changes, the total price will be automatically updated.
  • The total price calculation is straightforward: quantity multiplied by the price per item.
  • Initially, with a quantity of 1 and a price per item of 5, the total price is 5.
  • Subsequent clicks increase the quantity and update the total price accordingly.
  • To simplify the process and avoid unnecessary complexity, it's possible to calculate the total price directly within the function without using additional hooks like useState or useEffect.
  • Objects and arrays in JavaScript are passed by reference, leading to re-renders when updating an object due to React recognizing a change in the reference.
  • When setting state with an object, React may re-render due to the change in the object's reference, unlike with primitive values like numbers or strings.
  • Initializing state with null instead of undefined can prevent errors when accessing properties of an object before data is fetched.
  • In TypeScript, the type of a variable can be inferred based on its initial value, reducing the need for explicit type declarations in React components.

24:00

TypeScript Ensures Data Integrity and Type Safety

  • TypeScript infers data types, helping prevent errors in code by recognizing the correct type of variables.
  • When using methods like toUpperCase on variables, TypeScript ensures compatibility with the variable type.
  • TypeScript provides warnings when attempting incompatible operations on variables of incorrect types.
  • Setting state variables with incorrect types triggers TypeScript warnings, ensuring data integrity.
  • Primitive values like numbers are automatically inferred by TypeScript based on initial values.
  • Objects require explicit typing in TypeScript to ensure proper access to their properties.
  • Custom types can be created in TypeScript to define complex data structures.
  • TypeScript enforces type checking, highlighting mismatches between declared and assigned types.
  • Creating custom hooks in React helps avoid code duplication and enhances reusability.
  • React components can be designated as server or client components, affecting their behavior and access to certain features.

35:51

Managing State and Effects in JavaScript

  • Closure in JavaScript involves variables retaining their values at function creation time.
  • To ensure a variable updates every second, the function must be destroyed and recreated.
  • Adding the variable to a dependency array in useEffect allows for updates on change.
  • Without canceling previous intervals, adding new intervals can lead to unexpected results.
  • Using clearInterval and a cleanup function in useEffect prevents multiple intervals from stacking.
  • Fetching data in useEffect can lead to multiple fetch calls if not managed properly.
  • To avoid multiple fetch calls, use an AbortController to cancel previous fetches.
  • Fetching data in useEffect can lead to race conditions and other issues like caching and loading states.
  • Consider using libraries like react-query or SWR for better data fetching management in real-world applications.
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