This is the 21st day of my participation in the August Text Challenge.More challenges in August !

define

Solutions to asynchronous problems with synchronous thinking

  • Async precedes functions as a keyword

    • Any oneasyncAll functions implicitly return onepromise

  • The await keyword can only be used in functions defined using async

    • Await can be followed directly by a Promise instance object
    • The await function cannot be used alone

  • Async /await makes asynchronous code look and behave more like synchronous code

usage

Await is placed before the Promise call, and await forces the code to wait until the Promise object resolve returns the value of resolve as the result of the await expression

Await can only be used inside async functions, normal functions will get an error if used

async function a(){ console.log('a'); var a = await b(); // When await returns non-promise console.log('12'); } function b(){ console.log('b'); } // return undefined a();Copy the code

The role of async

The async function is responsible for returning a Promise object. If an async function returns an immediate quantity,

Async encapsulates this direct quantity into a Promise object via promise.resolve ();

If async does not return a value, it returns promise.resolve (undefined).

Await role

If an await waits for something other than a promise object, the result of the operation on the following expression is what it waits for

If it is a Promise object, await blocks subsequent code until the Promise object resolve

The way async await functions handle errors

1. Using a try… Catch statement

2. Add a catch callback to the Promise after await

Advantages over Promise

1. Serial synchronous writing method, code reading is relatively easy

2.Async/Await allows try/catch to handle both synchronous and asynchronous errors.

3. Advantage in code clarity when dealing with complex processes

GetAllCategory () {allAppConfig().then((pt) => {this.allapplist = pt.response this.ptname = pt.response[0].name this.ptId = pt.response[0].id getCopyCategory({ appId: this.ptId }).then((lm) => { this.getAllCategoryList = lm.response this.lmName = lm.response[0].categoryName this.categoryId = lm.response[0].categoryId this.getArticleList() }) }) }Copy the code

To:

async getAllCategory() {
    let pt = await allAppConfig()
    if (pt.code === 200) {
      this.allAppList = pt.response
      this.ptName = pt.response[0].name
      this.ptId = pt.response[0].id
    }
    let lm = await getCopyCategory({ appId: this.ptId })
    if (lm.code === 200) {
      this.getAllCategoryList = lm.response
      this.lmName = lm.response[0].categoryName
      this.categoryId = lm.response[0].categoryId
    }
    this.getArticleList()
  }
Copy the code