Lesson 4: Return Values

Learning Objectives

By the end of this lesson, learners will be able to:

• Understand what the return keyword does in a function
• Use return to send data back from a function
• Differentiate between return and console.log()
• Store and reuse return values in variables
• Build functions that produce useful results

What Is a Return Value?

In JavaScript, a function can give back a result using the return keyword. This value can then be:

• stored in a variable,
• used in calculations,
• passed into another function, and more.

Think of return as the “output” of a function — like how a calculator returns a result after a calculation.

Syntax

function functionName(parameters) {
  // code
  return value;
}

• return: ends the function and sends a value back
• The value can be a number, string, boolean, object, etc.

Example 1: Returning a Greeting

function getGreeting(name) {
  return "Hello, " + name + "!";
}

let message = getGreeting("Emma");
console.log(message); // Output: Hello, Emma!

• The function returns a string
• The result is stored in message and used later

Difference: return vs. console.log()

Example:

function add(a, b) {
  return a + b;
}

console.log(add(3, 4)); // Output: 7

• return a + b; sends the result back
• console.log(...) displays the result

Example 2: Reuse the Returned Value

function double(x) {
  return x * 2;
}

let result = double(5);
console.log("Double is:", result); // Output: Double is: 10

✅ You can now reuse the result for further logic.

Functions Stop After return

Any code written after the return statement won’t run:

function test() {
  return "Done";
  console.log("This won't run");
}

🧠 Always put return at the end if you want other code to run first.

Functions Without return

If a function doesn’t explicitly return something, it returns undefined by default:

function greet(name) {
  console.log("Hello, " + name);
}

let output = greet("Liam");
console.log(output); // Output: Hello, Liam  →  undefined

• greet() prints to the console
• But it returns nothing, so output is undefined

Summary