Functions in JavaScript

Functions are central in JavaScript. We’ll learn about functions with a few different examples.

// Here's a function that takes two numbers and returns
// their sum as a number.
function plus(a, b) {
    // JavaScript has implicit returns, but we'll use an explicit return
    // to maintain similarity with the original example.
    return a + b;
}

// In JavaScript, we don't need to specify types for parameters.
// Here's a function that takes three parameters and returns their sum.
function plusPlus(a, b, c) {
    return a + b + c;
}

// In JavaScript, we don't have a main function.
// Instead, we can just write our code at the top level.
// For demonstration purposes, we'll wrap it in an immediately invoked function expression (IIFE).
(function() {
    // Call a function just as you'd expect, with name(args).
    let res = plus(1, 2);
    console.log("1+2 =", res);

    res = plusPlus(1, 2, 3);
    console.log("1+2+3 =", res);
})();

To run this JavaScript code, you can save it in a file (e.g., functions.js) and run it using Node.js:

$ node functions.js
1+2 = 3
1+2+3 = 6

There are several other features to JavaScript functions. One is the ability to return multiple values using arrays or objects, which we’ll look at next.

Maps in JavaScript

Multiple Return Values in JavaScript

Learn X By Example

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Functions in JavaScript