Functions

Functions are the main unit of reuse in most programs. You give a piece of logic a name, and then call that name every time you want it to run — possibly with different inputs.

From this lesson on, the lesson checker runs tests that call your function with various inputs and compare what it returns. Make sure you return the answer — not just console.log it.

What you'll learn

• Declare a function with function name(params) { ... }
• Accept parameters and return a value
• Call a function and use its returned value

Instructions

Write a function named greet that takes one parameter name (a string) and returns a greeting string formatted like "Hello, World!".

Examples:

• greet("World") → "Hello, World!"
• greet("Ada") → "Hello, Ada!"
• greet("") → "Hello, !"

Use the Examples tab above the editor to see the tests your function has to pass. Click Run examples to run your code against them, and Check My Work to finalize.

Key concepts

Declaring a function

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

• function is the keyword that starts a declaration
• add is the function's name
• (a, b) are its parameters — local variables that get bound to whatever the caller passes in
• Whatever you return is the value that shows up where the call was written

Calling a function

const sum = add(3, 4);  // sum is now 7
console.log(sum);       // prints 7

return vs console.log

These are different things — a confusing early stumble.

function shout(msg) {
  console.log(msg);   // prints to the output — doesn't hand anything back
}

function shoutBetter(msg) {
  return msg.toUpperCase();   // hands a value back
}

const result = shout("hi");          // result is undefined
const result2 = shoutBetter("hi");   // result2 is "HI"

The lesson checker calls your function and inspects what it returned. A function that only console.logs will fail the tests — tests see whatever is returned, not whatever was printed.

Template literals are your friend

function greet(name) {
  return `Hello, ${name}!`;
}

Way easier than splicing with +.

Hints

1. You need function greet(name) { ... } — and inside, a single return.
2. The result should be formatted like Hello, X! where X is the name.
3. return \Hello, ${name}!\;