A JavaScript Immediately Invoked Function Expression (IIFE) is a function that executes immediately after it's defined, offering several benefits such as preventing global scope pollution by creating isolated scopes, which is particularly useful for libraries like jQuery. IIFEs also facilitate asynchronous operations and the creation of private variables, enhancing code organization and reducing errors. This tutorial guides readers through using IIFEs in JavaScript, testing these functions with Jest, and integrating continuous integration/continuous deployment (CI/CD) using CircleCI. It explains the importance of semicolon placement to avoid errors in JavaScript, highlights the distinction between named and anonymous IIFEs, and demonstrates the use of closures to maintain variable state across function calls. The tutorial includes practical exercises like cloning a GitHub repository, setting up a project with Node.js, installing dependencies, and configuring CircleCI to automate tests, ultimately showcasing how IIFEs can streamline JavaScript workflows.