3.2.1 Reading — Parameters & Return Values

Parameters & Return Values

What you'll learn:

• How parameters let you pass different inputs to the same function
• How return sends a value back out of a function
• How to store a returned value in a variable
• The difference between a function that prints vs one that returns

Parameters — giving a function inputs

A parameter is a variable listed inside the function's parentheses. When you call the function, the value you pass in becomes that variable inside the function.

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

greet("Alice");   // prints: Hello, Alice!
greet("Bob");     // prints: Hello, Bob!

The same function, two different results, because the input changed.

Return — getting a value back out

console.log inside a function prints something, but the result disappears. If you want to use the result later, use return:

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

let result = add(3, 4);
console.log(result);   // 7

return hands the value back to whoever called the function. You can then store it, print it, or use it in another expression.

Try it: Run the block. Then change the two numbers passed to add and run it again.

Both lines output 15, but they work differently. The first stores the result in result so you could use it again. The second just prints and the value is gone.

Short glossary (quick reference)