Promise

Promise - JavaScript | MDN

How do Promises Work? - Quil’s Fluffy World

• Japanese translation: How Promise works - Implementing Promise | POSTD Good commentary, but the Japanese translation is not very good.

For Promise - JavaScript | MDN on 6/2019

• The term “resolve is called asynchronously” is ambiguous. I wrote, but now that I look at it, I couldn’t find that expression. As of 2021/2, it is written more clearly.

• Note that promises are guaranteed to be asynchronous. Thus, an action on a promise that has already been “resolved” will be executed only after the stack has been cleared and a clock tick has elapsed. This effect is very similar to setTimeout(action,10) ---old The term “resolve is called asynchronously” is ambiguous.

• The first argument of Promise, (resolve, reject) ⇒ {…} Whether you call resolve synchronously or asynchronously in

:

create promise start
promise body start
sync body start
sync body end
promise body end
create promise end
specify promise.then start
specify promise.then end
resolved ok

ts

  const syncBody = (resolve: any, reject: any) => {
    console.log("sync body start")
    resolve("ok")
    console.log("sync body end")
  }
  const asyncBody = (resolve: any, reject: any) => {
    console.log("async body start")
    setTimeout(() => {
      console.log("timeout start")
      resolve("ok")
      console.log("timeout end")
    }, 1000)
    console.log("async body end")
  }
 
  console.log("create promise start")
  let p = new Promise((resolve, reject) => {
    console.log("promise body start")
    syncBody(resolve, reject)
    console.log("promise body end")
  })
  console.log("create promise end")
 
  console.log("specify promise.then start")
  p.then((x) => {
    console.log("resolved", x)
  })
  console.log("specify promise.then end")

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