Promise在Node JS中是同步还是异步 [英] Promise is synchronous or asynchronous in node js

问题描述

我对诺言充满困惑.是同步还是异步?

I have lot of confusion in promise. It's a synchronous or asynchronous ?

return new Promise (function(resolved,reject){
    //sync or async? 
});

推荐答案

您将传递给的函数Promise构造函数是同步运行的，但是取决于其分辨率的任何内容都将被异步调用.即使promise立即解决，任何处理程序都将异步执行(类似于setTimeout(fn, 0)时)-主线程首先运行到末尾.

The function you pass into the Promise constructor runs synchronously, but anything that depends on its resolution will be called asynchronously. Even if the promise resolves immediately, any handlers will execute asynchronously (similar to when you setTimeout(fn, 0)) - the main thread runs to the end first.

无论您是使用Javascript环境还是使用Node还是浏览器，都是如此.

This is true no matter your Javascript environment - no matter whether you're in Node or a browser.

console.log('start');
const myProm = new Promise(function(resolve, reject) {
  console.log('running');
  resolve();
});
myProm.then(() => console.log('resolved'));
console.log('end of main block');

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