JavaScript Fundamentals · Async JavaScript · Lesson 27 of 48
Promises
Concept
Promises
A Promise represents a value that will be available now, later, or never. then() handles success and catch() handles failure.
A Promise is always in one of three states — pending, fulfilled, or rejected — and once it settles into fulfilled or rejected, it never changes state again.
- Explain the core idea behind Promises.
- Predict output before running a change.
- Test one realistic and one unusual input.
- Use the result to make the next decision.
- 1. Read one concept.
- 2. Change the example.
- 3. Run, compare, and explain.
- 4. Complete the challenge below.
Self-check before continuing
Without looking at the example, describe what changes when you modify one input in Promises. 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
Write a Promise that resolves with your name after 1 second.
Ask about this lesson or your next move. The guide explains the path without taking the work away from you.
Ready for the next lesson?
Mark this lesson complete when you have finished the exercise.
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