JavaScript Fundamentals · Functions · Lesson 13 of 48
Parameters and Return Values
Concept
Parameters and Return Values
Parameters are placeholders for input values. return sends a result back to wherever the function was called.
As soon as return runs, the function stops immediately — any code written after it in the same block never executes.
By the end of this lesson
- Explain the core idea behind Parameters and Return Values.
- 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.
Syntax
function name(param1, param2) {
return param1 + param2;
}ExampleRunnable
function add(a, b) {
return a + b;
}
const total = add(4, 7);
console.log(total);Default parameter values
function greet(name = "friend") {
return "Hi, " + name;
}
console.log(greet());Note: A default value is used only when the argument is omitted entirely, or passed as undefined.
Self-check before continuing
Without looking at the example, describe what changes when you modify one input in Parameters and Return Values. 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 function that takes three numbers and returns their average.
Loading editor…
Console