NodeJS - setTimeout(fn,0) vs setImmediate(fn)

Question

What is the difference between those two, and when will I use one over the other?

Answer 1

setImmediate() is to schedule the immediate execution of callback after I/O events callbacks and before setTimeout and setInterval .

setTimeout() is to schedule execution of a one-time callback after delay milliseconds.

This is what the documents say.

setTimeout(function() {
  console.log('setTimeout')
}, 0)

setImmediate(function() {
  console.log('setImmediate')
})

If you run the above code, the result will be like this... even though the current doc states that "To schedule the "immediate" execution of callback after I/O events callbacks and before setTimeout and setInterval." ..

Result..

setTimeout

setImmediate

If you wrap your example in another timer, it always prints setImmediate followed by setTimeout.

setTimeout(function() {
  setTimeout(function() {
    console.log('setTimeout')
  }, 0);
  setImmediate(function() {
    console.log('setImmediate')
  });
}, 10);