The event loop is what makes the Node so fast and brilliant. It helps the Node utilize the time efficiently which otherwise would have been wasted while waiting for input and output tasks to complete. The event loop is what makes the Node great at optimizing I/O-bound systems. If your Node.js app needs to perform something CPU-intensive for example computation, hashing of passwords or compressing, then besides the usual task of spawning new processes for CPU-tasks, you will also require to explore options for deferring of the task with setImmediate() or setTimeout(). The code in their callbacks will continue on the next event loop cycle. Unfortunately, nextTick() works on the same cycle contrary to the name.
Because the scripting engine needs to look through the scope when referencing global variables from within function or another scope, the variable will be destroyed when the local scope is lost. If variables in the global scope can not persist through the lifetime of the script, the performance will be improved.
Accessing the DOM is slow. If you are going to read the content of an element several times, it's better to save it in a local variable. But it’s important to keep in mind, if you will later remove the value of the DOM, the variable should be set to "null", so it doesn’t cause any memory leaks.
According to the Mozilla Developers Network (MDN) documentation: “Web Workers makes it possible to run a script operation in a background thread separate from the main execution thread of a web application. The advantage of this is that laborious processing can be performed in a separate thread, allowing the main (usually the UI) thread to run without being blocked/slowed down.” Web workers allow your code to perform processor-intensive calculations without blocking the user interface thread. Web Workers allow you spawn new threads and delegate work to these threads for efficient performance. This way, long running tasks which would normally block other tasks are passed off to a worker and the main thread can run without being blocked.
If a memory leak is ongoing, the loaded page will reserve more and more memory, eventually occupying all the available memory of the device and severely impacting performance. You’ve probably seen (and likely been frustrated by) this type of failure, likely on a page with a carousel or image slider. In Chrome Dev Tools, you can analyze if your website has memory leaks by recording a timeline in the Performance tab. Usually, memory leaks come from pieces of the DOM that are removed from the page but have some variable that makes reference to them and, therefore, the garbage collector can not eliminate them.