在 process.nextTick() 函数之后未调用 setImmediate() 函数答案

【问题标题】：setImmediate() function not being called after process.nextTick() function在 process.nextTick() 函数之后未调用 setImmediate() 函数
【发布时间】：2018-09-12 00:57:58
【问题描述】：

对于这个sn-p：

const foo = [1, 2];
const bar = ['a', 'b'];

foo.forEach( num => {
  console.log(`setting setImmmediate ${num}`);
  setImmediate(() => {
    console.log(`running setImmediate ${num}`);
    bar.forEach(char => {
      console.log(`setting nextTick ${char}`);
      process.nextTick(() => {
        console.log(`running nextTick ${char}`);
      })
    })
  });
} )

输出是

$ node scratch.js                   
setting setImmmediate 1
setting setImmmediate 2
running setImmediate 1
setting nextTick a
setting nextTick b
running setImmediate 2
setting nextTick a
setting nextTick b
running nextTick a
running nextTick b
running nextTick a
running nextTick b

来自docs

nextTickQueue 将在当前操作完成后处理，与事件循环的当前阶段无关。

据我了解，process.nextTick() 将添加到当前事件的nextTickQueue，并在当前事件之后立即执行，无论事件循环处于哪个阶段。

输出不应该是下面的吗？

setting setImmmediate 1
setting setImmmediate 2
running setImmediate 1
setting nextTick a
setting nextTick b
running nextTick a
running nextTick b
running setImmediate 2
setting nextTick a
setting nextTick b
running nextTick a
running nextTick b

【问题讨论】：

标签： node.js event-loop libuv

【解决方案1】：

nextTickQueue 将在 当前操作 完成后处理，与事件循环的当前阶段无关。

我误解了event loop documentation 认为“当前操作”是指当前正在处理的事件，而实际上它是指当前正在处理的阶段。

来自 Danial Khan 的What you should know to really understand the Node.js Event Loop/：

【讨论】：