As mentioned earlier, the code of Node.js is NOT executed in parallel. It’s important to differentiate between CPU operations and I/O (input/output) operations. The golden rule: don’t block the event loop, try to keep it running it and pay attention and avoid anything that could block the thread like synchronous network calls or infinite loops. A “Non-blocking” function will allow the main event loop to continue as soon as it begins and typically alerts the main loop once it has finished by calling a “callback”. Similarly, If you are making a request to a server that has CPU-intensive code, that code can block the event loop and prevent other requests of being handled.Ī function is considered “blocking” if the main event loop must wait until it has finished executing the next command. The reason it was built with that approach is that JavaScript was initially created for client-side interactions (like web page interactions, or form validation) - nothing that required the complexity of multithreading.īut, as with all things, there is a downside: if you have CPU-intensive code, like complex calculations in a large dataset taking place in-memory, it can block other processes from being executed. This is very useful because it simplifies how you use JavaScript without worrying about concurrency issues. One code, one execution, (the code is not executed in parallel). In other words, Node runs on a single thread, and there is just one process happening at a time in the event loop. One Node.js Instance: the computer program that executes Node.js code. One JS Engine Instance: this is a computer program that executes JavaScript code. It’s what allows Node to be asynchronous and have non-blocking I/O, - despite the fact that JavaScript is single-threaded - by offloading operations to the system kernel whenever possible through callbacks, promises and async/await. One event loop: this is one of the most important aspects to understand about Node. One thread: being single-threaded means that only one set of instructions is executed at a time in a given process. One process: a process is a global object that can be accessed anywhere and has information about what’s being executed at a time. When a Node.js process is launched, it runs: To understand Workers, first, it’s necessary to understand how Node.js is structured.
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