Node.js synchronous and asynchronous programming

Synchronous API: API currently only after the execution is complete, before proceeding to the next line API. From top to bottom, line by line execution.

console.log("one")

console.log("two")

 

Asynchronous API: The API currently does not block the subsequent execution of the code.

 console.log("one")

setTimeout ( () =>  console.log("two"), 3000)

console.log("three")

 

Synchronous asynchronous API API difference (the return value acquisition)

Synchronization API API can get the execution result from the return value, but not the asynchronous API.

// 同步

function sum (a, b) {
  return a+ b  
}

 

// 异步

function getMsg () {
  setTimeout( function () {
    console.log('hello node.js')  
  })   
}

 

Asynchronous API to get data (callback)

 1 function getMsg (fn) {
 2   setTimeout(function () {
 3     fn({
 4       msg: 'hello'
 5     })
 6   }, 3000)
 7 }
 8 
 9 getMsg(function (data) {
10   console.log(data)
11 })