Function
In one line
A function is a reusable block of code that performs a task, optionally taking inputs and returning a result.
In simple words
A function is a named, reusable block of code. You write it once, then call it by name whenever you need it — optionally passing in inputs (parameters) and getting a result (return value) back.
Functions help you avoid repeating yourself (the DRY principle). Instead of writing the same calculation in five places, you write it once as a function and call it five times. If the logic changes, you update only the function.
Functions are the primary way programmers organize and structure code. A typical program is a collection of functions that call each other, each focused on one small job.
Example
function add(a, b) {
return a + b;
}
console.log(add(2, 3)); // 5
console.log(add(10, 20)); // 30add is a function that takes two parameters a and b and returns their sum.
How it works
- Define the function with a name and a body (the code to run).
- Call the function by name, optionally passing arguments.
- The function runs its body, using the arguments as inputs.
- If the function has a
returnstatement, it sends a value back to the caller.
Common confusions
Confused with: method
The difference: A function stands on its own; a method is a function that belongs to an object and is called with a dot (e.g. array.push()). All methods are functions, but not all functions are methods.
Related terms
Related Resources
Related Lessons
- Functions
Learn how to define and call functions
Related Practice
Related Projects
- Simple Calculator
Build a calculator using functions for each operation
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