小编tus*_*har的帖子

我已阅读官方文档和许多其他博客，process.nextTick()但我对某些主题有点困惑。

首先，写入中的回调process.nextTick()在下一次迭代开始之前执行。

其次，当在 I/O 周期内时，事件循环当前处于轮询阶段。在轮询阶段之后，事件循环进入检查阶段，在该阶段执行setImmediate方法中调用的任何回调。

现在在下面的代码中

const fs = require('fs');

function main() {
   fs.readFile('./xy.txt', function(err, buff){
      setTimeout(()=> console.log("timeout inside fs"),0);
      setImmediate(()=> console.log("immediate inside fs"));
      process.nextTick(()=>{console.log("process.nextTick")});
      console.log("inside fs");
   })
   console.log("called inside main fn in first-iteration");
}

main();
console.log("called in first-iteration);

输出将是：

const fs = require('fs');

function main() {
   fs.readFile('./xy.txt', function(err, buff){
      setTimeout(()=> console.log("timeout inside fs"),0);
      setImmediate(()=> console.log("immediate inside fs"));
      process.nextTick(()=>{console.log("process.nextTick")});
      console.log("inside fs");
   })
   console.log("called inside main fn in first-iteration");
}

main();
console.log("called in first-iteration);

在此期间， …