JavaScript Fundamentals · Functions · Lesson 15 of 48
Scope
Concept
Scope
Variables declared inside a function only exist inside that function, which is called local scope. Variables declared outside are global.
This isolation is a feature: it means two different functions can each safely use a variable named total without interfering with each other.
- Explain the core idea behind Scope.
- 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 Scope. 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
Predict and then test what happens if you try to log the inside variable outside the function.
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.
Console