The text discusses the evolution and implementation of multithreading in JavaScript, focusing on the worker_threads module in Node.js. Historically, JavaScript was single-threaded, which made it simpler for adding interactivity to web pages, but presented challenges for handling CPU-intensive tasks, leading to potential blocking issues. Node.js, initially designed for asynchronous I/O, introduced worker_threads to facilitate parallel processing without shared memory, thus avoiding race conditions. Worker threads allow for CPU-bound tasks to run in isolated contexts, communicating with the main process through message passing. To optimize resource usage, developers often use worker pools to manage multiple threads efficiently. Alternatives to worker_threads, such as thread pools, child processes, and clustering, are also explored for specific use cases. Additionally, the text compares worker threads with the Web Workers API, which serves a similar purpose in web browsers, and highlights Partytown as a solution for running third-party scripts separately from the main thread to maintain UI responsiveness.