JavaScript Tutorial
Functions are the building blocks of JavaScript programs.
They let you organize logic, reuse behavior, and write cleaner code.
Without functions, code becomes repetitive and difficult to maintain.
Functions help you structure programs and make your logic reusable.
function name(params) { ... }
const name = function(params) { ... }
const name = (params) => { ... }function greet(name) {
return "Hello " + name;
}
console.log(greet("Ava"));Define a function once and reuse it.
const add = (a, b) => a + b;
console.log(add(2, 3));Arrow functions are concise for small logic.
Functions let you package logic into reusable blocks. You can call them whenever you need the same behavior.
This keeps code DRY and easier to maintain.
Parameters are inputs to a function. Return values are outputs.
Clear inputs and outputs make functions predictable and testable.
JavaScript supports declarations, expressions, arrow functions, and IIFEs.
Each style has different use cases for readability and context binding.
Callbacks let functions accept other functions as arguments.
Higher-order functions return functions or accept them, enabling powerful patterns.
function run(task) {
task();
}
run(() => console.log("Done"));Pass functions as arguments for flexible behavior.
function makeMultiplier(factor) {
return (value) => value * factor;
}
const double = makeMultiplier(2);
console.log(double(5));Return functions to create reusable behaviors.
Without
const price1 = 10 * 1.18;
const price2 = 20 * 1.18;With
function addTax(amount) {
return amount * 1.18;
}
const price1 = addTax(10);
const price2 = addTax(20);Split logic into smaller, focused functions.
Return values make functions easier to compose.
Pass data via parameters instead of globals.
Choose the style that matches your use case and stick to it.
Parameters are named inputs; arguments are actual values passed in.
A function that takes or returns another function.
A function calling itself to solve a smaller version of a problem.
Practice: Write a function that takes a price and a tax rate and returns the total.
// TODO: implement addTax
One Possible Solution
function addTax(price, rate) {
return price + price * rate;
}
console.log(addTax(100, 0.18));A reusable block of code that can take inputs and return outputs.
When you need short functions or lexical this binding.
A function passed as an argument to be called later.
Try calling the function with different names and see the output.