JavaScript — Lesson 3
Functions
Reusable blocks of code.
Functions
Functions are reusable blocks of code that perform specific tasks. They help you organize and reuse your code.
Function Declaration
// Define a function
function greet() {
console.log("Hello!");
}
// Call (invoke) the function
greet(); // Output: Hello!
Parameters & Arguments
// name is a parameter
function greet(name) {
console.log("Hello, " + name + "!");
}
// "Alice" is an argument
greet("Alice"); // Output: Hello, Alice!
Return Values
function add(a, b) {
return a + b;
}
const sum = add(5, 3); // sum = 8
Arrow Functions (ES6)
A shorter syntax for writing functions.
// Traditional function
const double = function(n) {
return n * 2;
};
// Arrow function (shorter)
const double = (n) => {
return n * 2;
};
// Even shorter (implicit return)
const double = n => n * 2;
Default Parameters
function greet(name = "Guest") {
console.log("Hello, " + name + "!");
}
greet(); // Hello, Guest!
greet("Bob"); // Hello, Bob!
Why Use Functions?
- Reusability: Write once, use many times
- Organization: Break complex code into smaller pieces
- Readability: Named functions describe what they do
- Testing: Small functions are easy to test
Tip: A function should do one thing and do it well. If a function does too many things, split it into smaller functions.
Practice what you learned in the Deoit Editor — a free, browser-based code editor.
Open Editor →