Understanding setImmediate()

The Node.js setImmediate function interacts with the event loop in a special way

When you want to execute some piece of code asynchronously, but as soon as possible, one option is to use the setImmediate() function provided by Node.js:

setImmediate(() => {
  //run something
})

Any function passed as the setImmediate() argument is a callback that’s executed in the next iteration of the event loop.

How is setImmediate() different from setTimeout(() => {}, 0) (passing a 0ms timeout), and from process.nextTick()?

A function passed to process.nextTick() is going to be executed on the current iteration of the event loop, after the current operation ends. This means it will always execute before setTimeout and setImmediate.

A setTimeout() callback with a 0ms delay is very similar to setImmediate(). The execution order will depend on various factors, but they will be both run in the next iteration of the event loop.