Redux & Redux Toolkit Course
Redux & Redux Toolkit
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Beginner

Immutable State Updates

Definition

The requirement in React and Redux that state objects must never be directly modified. Instead, a new copy of the object must be created with the desired changes.

Explain Like I'm New

If you have a piece of paper, you cannot erase what is written on it. To make a change, you must place a brand new piece of paper over it, trace everything exactly, and draw your new changes on the new paper. The old paper remains untouched.

Real World Example

Using the spread operator `[...oldArray, newItem]` instead of `oldArray.push(newItem)`.

Common Use Cases

  • •React rendering triggers
  • •Time travel debugging

Interactive Example

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Interview Questions

basic

  • Why does React require immutable updates?

intermediate

  • What happens if you accidentally mutate an array using `.push()` in plain Redux?

Flash Cards

Question

Why?

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Answer

Because of reference equality (`===`). React is fast because it doesn't compare the actual data deeply. It just checks if the memory address of the object changed. If you mutate the object, the memory address stays the same, and React assumes the data hasn't changed, causing your UI to freeze.

Question

What happens?

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Answer

The state inside the Redux store will actually change, but React will NOT re-render. Your screen will show outdated data.