Intro to multithreaded JavaScript
The JavaScript language is one of the wonders of the software world. It is incredibly powerful, flexible, and versatile. One limitation of its fundamental design, however, is its single-threaded nature. Traditional JavaScript appears to handle parallel tasks, but that is a trick of syntax. To achieve true parallelism, you need to use modern multithreading approaches like web workers and worker threads.
Parallelism vs. concurrency
The most basic way to understand the difference between parallelism and concurrency is that concurrency is semantic whereas parallelism is implementation. What I mean is that concurrency lets you tell the system (semantics) to do more than one thing at once. Parallelism simply performs multiple tasks simultaneously (implementation). All parallel processing is concurrent, but not all concurrent programming is parallel.