Updating arrays in state

What this means

When an array is stored in state, create a new array instead of mutating the old one. Use methods like spread, filter, and map.

In beginner terms, this topic answers one practical question: "What should I write, and why does React care about it?" Do not try to memorize the syntax first. First understand the idea, then connect the syntax to that idea.

Why it matters

React compares old and new values. Creating a new array makes the change clear and predictable.

When you build real React screens, this idea helps you decide where data should live, what the user should see, and what should happen after an interaction. That is why this lesson is part of the main path instead of being an optional detail.

Step by step

1. Notice the UI problem this topic solves. 2. Look at the smallest possible example. 3. Change one value and predict what should appear. 4. Run the example and compare the result with your prediction. 5. Use the practice task before moving on.

Small example

setTasks([...tasks, newTask]);
setTasks(tasks.filter((task) => task.id !== id));

Common mistake

Do not call mutating methods like push on state arrays and then expect React to notice reliably.

Practice task

Create a task list with a button that adds one new task using the spread operator.

Remember this

Update arrays by creating new arrays.