1.Async/Await Introduction

With async/await, you can easily do what the previous promises do, it has the following characteristics:
• async/await is based on Promise and is not used for normal callback functions.
• async/await, like Promise, is non-blocking.
• async/await makes asynchronous code look like synchronous code, which is where its magic lies.
If a function adds async , the function will return a Promise

async function async1() {
  return "1"
}
console.log(async1()) // -> Promise {<resolved>: "1"}

async1().then(function(data){
     Console.log(data);  // -> 1
});

Calling three files in turn, the example is written in async/await, which can be implemented in just a few sentences.

var fs = require('fs');

function read(file) {
  return new Promise(function(resolve, reject) {
    fs.readFile(file, 'utf8', function(err, data) {
      if (err) reject(err)
      resolve(data)
    })
  })
}
async function readResult(params) {
  try {
         Var p1 = await read(params, 'utf8')//await followed by a Promise instance
    var p2 = await read(p1, 'utf8')
    var p3 = await read(p2, 'utf8')
    console.log('p1', p1)
    console.log('p2', p2)
    console.log('p3', p3)
    return p3
  } catch (error) {
    console.log(error)
  }
}
 readResult('1.txt').then( // async function returns a promise
  data => {
    console.log(data)
  },
  err => console.log(err)
)

2.Async/Await concurrent request

If you request two files, it doesn't matter, you can pass the concurrent request.

var fs = require('fs');

function read(file) {
  return new Promise(function(resolve, reject) {
    fs.readFile(file, 'utf8', function(err, data) {
      if (err) reject(err)
      resolve(data)
    })
  })
}
function readAll() {
  read1()
  Read2 () / / this function synchronous execution
}
async function read1() {
  let r = await read('1.txt','utf8')
  console.log(r)
}
async function read2() {
  let r = await read('2.txt','utf8')
  console.log(r)
}
readAll();

3. Async/await refactors the user management system data persistence operation code (ie database operation)3, summary

1.JS asynchronous programming evolution history: callback -> promise -> generator -> async + await
2. The implementation of the async/await function is to wrap the Generator function and auto-executor in a function.
3.async/await can be said to be the ultimate asynchronous solution.
(1) The advantage of the async/await function over Promise is that:
• Handle the call chain of then to write the code more clearly and accurately
• It also elegantly solves the callback hell problem.
Of course, the async/await function also has some drawbacks, because await transforms asynchronous code into synchronous code. If multiple asynchronous code has no dependencies, using await will result in performance degradation. If the code has no dependencies, you can use the Promise.all method.