Self-invoking. Learn JavaScript!
This type of JavaScript function is known as self-invoking or immediately-invoked function expression (IIFE). It is a function that is defined and executed at the same time, without being assigned to a variable or being called by another function. It is often used to create a local scope for variables and avoid polluting the global namespace. References: [W3Schools - JavaScript Function Definitions], [MDN Web Docs - Immediately-invoked function expressions]