Writing Functions

A function is a named block of code that does a job. You write it once, then call it whenever you need that job done. This saves you from repeating yourself.

Defining a function

function sayHello() {
  console.log("Hello there!");
}

sayHello(); // this runs the function

The word function starts the definition, sayHello is the name, the ( ) hold inputs (none yet), and the code lives inside the { }. Writing sayHello() on its own line calls the function, telling it to run.

Giving a function inputs

Functions become really useful when you pass them information. These inputs are called parameters.

function greet(name) {
  console.log(`Hello, ${name}!`);
}

greet("Alex");
greet("Sam");

The same function now greets anyone you give it.

Getting an answer back

A function can hand a value back to you using return. You can then store or print that result.

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

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

Try it yourself

Call the functions with different inputs and see what comes back.