# Working with Functions

A JavaScript function is declared with the function keyword, and has no return type and no parameter types. A missing argument is undefined, an extra one is ignored, and a function with no return gives undefined. Functions are values, too.

![Cheat sheet: Working with Functions](https://fsdtrainingmedia.blob.core.windows.net/public/images/2026/11/0ab92501a2a6415c99a6a287b9c50648.webp)

- Category: JavaScript
- Level: Apprentice
- Tags: Callback Function, Default Parameter, Function Declaration, JavaScript, NaN, undefined
- Updated: November 3, 2026

Source: https://www.ask-codey.com/cheat-sheets/csharp-vs-javascript-working-with-functions-cheat-sheet