JavaScript Fundamentals · Loops · Lesson 10 of 48
while Loops
Concept
while Loops
A while loop repeats as long as a condition stays true, which is useful when you do not know exactly how many iterations you will need.
Because the condition is checked before every pass, a while loop can also run zero times if the condition is already false the first time it's checked.
- Explain the core idea behind while Loops.
- 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 while Loops. 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 while loop that keeps doubling a number starting from 1 until it exceeds 100.
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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