JavaScript详解使用Promise处理回调地狱的两种方法

import thenFs from "then-fs"
thenFs.readFile("./fis/1.txt","utf8").then(r1=>{
  console.log(r1);
})
thenFs.readFile("./fis/2.txt","utf8").then(r2=>{
  console.log(r2);
})
thenFs.readFile("./fis/3.txt","utf8").then(r3=>{
  console.log(r3);
})

import thenFs from "then-fs"
thenFs.readFile("./fis/1.txt","utf8").then(r1=>{
  console.log(r1);
  return thenFs.readFile("./fis/2.txt","utf8")
}).then(r2=>{
  console.log(r2);
  return thenFs.readFile("./fis/3.txt","utf8")
}).then(r3=>{
  console.log(r3);
})

import thenFs from "then-fs"
thenFs.readFile("./fis/11.txt","utf8").catch(err=>{
  console.log(err.message);
}).then(r1=>{
  console.log(r1);
  return thenFs.readFile("./fis/2.txt","utf8")
}).then(r2=>{
  console.log(r2);
  return thenFs.readFile("./fis/3.txt","utf8")
}).then(r3=>{
  console.log(r3);
})

import thenFs from "then-fs"
 async function getFile(){
// 不加await，打印的r1是一个promise实例对象，加await打印的是结果
const r1=await thenFs.readFile("./fis/1.txt","utf8")
console.log(r1);
const r2=await thenFs.readFile("./fis/2.txt","utf8")
console.log(r2);
const r3=await thenFs.readFile("./fis/3.txt","utf8")
console.log(r3);
 }
 getFile()

import thenFs from "then-fs"
// 在async方法中，第一个await之前的代码会同步执行，await之后的代码会异步执行
console.log("a");
 async function getFile(){
  console.log("b");
const r1=await thenFs.readFile("./fis/1.txt","utf8")
console.log(r1);
const r2=await thenFs.readFile("./fis/2.txt","utf8")
console.log(r2);
const r3=await thenFs.readFile("./fis/3.txt","utf8")
console.log(r3);
console.log("d");
 }
 getFile()
 console.log("c");