React Essentials · Final Project · Lesson 25 of 26
Building the Core Feature
Concept
Building the Core Feature
Start with the core interaction, like adding a todo, before adding extras like filtering or persistence.
By the end of this lesson
- Explain the core idea behind Building the Core Feature.
- Predict output before running a change.
- Test one realistic and one unusual input.
- Use the result to make the next decision.
How to study this page
- 1. Read one concept.
- 2. Change the example.
- 3. Run, compare, and explain.
- 4. Complete the challenge below.
ExampleRunnable
function addTodo(text) {
setTodos([...todos, { id: Date.now(), text }]);
}Self-check before continuing
Without looking at the example, describe what changes when you modify one input in Building the Core Feature. Then reopen the editor and prove your explanation with a small test.
You are ready to continue when you can predict, test, and explain the result.
Your turn
Implement an addItem function for your project's main list.
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Console