Functions
Functions are reusable blocks of code you can call by name.
Syntax
function name() { ... }
name();A function is a reusable block of code. You define it once and call it whenever you need it.
Declaring and calling
Use the function keyword, a name, parentheses, and a body in braces. Call it by writing its name followed by ().
Example
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When to use it
- Encapsulate a tax calculation so it can be called from multiple places in a checkout module.
- Define a reusable greeting function that the marketing page calls for each visitor segment.
- Wrap repeated DOM manipulation steps into a named function to keep event handlers short.
More examples
Declare and call a function
Declares a named function and calls it twice with different arguments.
function greet(name) {
console.log("Hello, " + name + "!");
}
greet("Alice"); // Hello, Alice!
greet("Bob"); // Hello, Bob!Function expression stored in variable
Assigns an anonymous function expression to a const variable and calls it by that variable name.
const square = function (n) {
return n * n;
};
console.log(square(5)); // 25Reusable tax calculator
Defines a function that computes a tax-inclusive total, making it reusable across the checkout flow.
function calculateTotal(price, taxRate) {
return price + price * taxRate;
}
const total = calculateTotal(49.99, 0.08);
console.log(total.toFixed(2)); // "53.99"
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