setImmediate vs. nextTick

Question

Node.js version 0.10 was released today and introduced setImmediate. The API changes documentation suggests using it when doing recursive nextTick

Answer 1

Some great answers here detailing how they both work.

Just adding one that answers the specific question asked:

When should I use nextTick and when should I use setImmediate?

---

Always use setImmediate.

---

The Node.js Event Loop, Timers, and process.nextTick() doc includes the following:

We recommend developers use setImmediate() in all cases because it's easier to reason about (and it leads to code that's compatible with a wider variety of environments, like browser JS.)

---

Earlier in the doc it warns that process.nextTick can lead to...

some bad situations because it allows you to "starve" your I/O by making recursive process.nextTick() calls, which prevents the event loop from reaching the poll phase.

As it turns out, process.nextTick can even starve Promises:

Promise.resolve().then(() => { console.log('this happens LAST'); });

process.nextTick(() => {
  console.log('all of these...');
  process.nextTick(() => {
    console.log('...happen before...');
    process.nextTick(() => {
      console.log('...the Promise ever...');
      process.nextTick(() => {
        console.log('...has a chance to resolve');
      })
    })
  })
})

On the other hand, setImmediate is "easier to reason about" and avoids these types of issues:

Promise.resolve().then(() => { console.log('this happens FIRST'); });

setImmediate(() => {
  console.log('this happens LAST');
})

---

So unless there is a specific need for the unique behavior of process.nextTick, the recommended approach is to "use setImmediate() in all cases".