JavaScript · Quick Reference

Lesson 7 — Functions Cheat Sheet

JavaScript

In one line: A function is a named, reusable block of code that performs a specific task. You define it once and call it as many times as you need. Think of a function as a recipe: you write...

Key Ideas

1What is a Function?. A function is a named, reusable block of code that performs a specific task. You define it once and call it as many times as you need. Think of a function as a recipe:...

2Function Declarations. The classic way to create a function uses the function keyword, followed by a name, parentheses for parameters, and a block body. The defining feature of declarations ...

3Function Expressions. A function expression assigns an anonymous (or named) function to a variable. Unlike declarations, function expressions are not hoisted — you can only call them after ...

4Arrow Functions (ES6). Arrow functions, introduced in ES2015, provide a shorter syntax for writing function expressions. They use the => token instead of the function keyword. Beyond brev...

5Parameters & Arguments. Parameters are the named placeholders in the function definition. Arguments are the actual values you pass when calling the function. JavaScript is flexible: you can p...

Code Examples

// Hoisting demo: call before definition works!
console.log(greet("Alice")); // Works! "Hello, Alice!"

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

// Multi-parameter function
function add(a, b) {
  return a + b;
}
console.log(add(3, 7)); // 10

/...

// Function expression — NOT hoisted
const multiply = function(a, b) {
  return a * b;
};

console.log(multiply(4, 6)); // 24

// Named function expression (useful in stack traces)
const factorial = function calcFactorial(n) {
  if (n <= 1) return 1;
  r...

// Full arrow function
const add = (a, b) => {
  return a + b;
};

// Implicit return (single expression — no braces, no return)
const double = x => x * 2;
console.log(double(7)); // 14

// No params: use empty parens
const greet = () => "Hello, Wo...