function findItem() {
    var item;
    while(item_not_found) {
        // search
    }
    return item;
}

var item = findItem();

// Do something with item
doSomethingElse();

findItem(function(item) {
    // Do something with the item
});
doSomethingElse();

---

---

重要: 您只能在一个 async 函数或 JavaScript 模块中使用等待。 顶级等待不支持模块之外,因此您可能需要创建一个 async IIFE (即时邀请函数表达) 以启动一个 async 背景,如果不使用模块。

// Using 'superagent' which will return a promise.
var superagent = require('superagent')

// This is isn't declared as `async` because it already returns a promise
function delay() {
  // `delay` returns a promise
  return new Promise(function(resolve, reject) {
    // Only `delay` is able to resolve or reject the promise
    setTimeout(function() {
      resolve(42); // After 3 seconds, resolve the promise with value 42
    }, 3000);
  });
}

async function getAllBooks() {
  try {
    // GET a list of book IDs of the current user
    var bookIDs = await superagent.get('/user/books');
    // wait for 3 seconds (just for the sake of this example)
    await delay();
    // GET information about each book
    return superagent.get('/books/ids='+JSON.stringify(bookIDs));
  } catch(error) {
    // If any of the awaited promises was rejected, this catch block
    // would catch the rejection reason
    return null;
  }
}

// Start an IIFE to use `await` at the top level
(async function(){
  let books = await getAllBooks();
  console.log(books);
})();

---

var result = foo();
// Code that depends on 'result'

foo(function(result) {
    // Code that depends on 'result'
});

function myCallback(result) {
    // Code that depends on 'result'
}

foo(myCallback);

function foo(callback) {
    $.ajax({
        // ...
        success: callback
    });
}

function foo(callback) {
    $.ajax({
        // ...
        success: function(response) {
            // For example, filter the response
            callback(filtered_response);
        }
    });
}

---

更多关于承诺的信息: HTML5 Rocks - JavaScript 承诺。

副注:jQuery的废弃物品

function ajax() {
    return $.ajax(...);
}

ajax().done(function(result) {
    // Code depending on result
}).fail(function() {
    // An error occurred
});

function checkPassword() {
    return $.ajax({
        url: '/password',
        data: {
            username: $('#username').val(),
            password: $('#password').val()
        },
        type: 'POST',
        dataType: 'json'
    });
}

if (checkPassword()) {
    // Tell the user they're logged in
}

但修正很容易:

checkPassword()
.done(function(r) {
    if (r) {
        // Tell the user they're logged in
    } else {
        // Tell the user their password was bad
    }
})
.fail(function(x) {
    // Tell the user something bad happened
});

---

不推荐:同步“Ajax”通话

正如我提到的那样,一些(!)无同步操作有同步对手,我不支持它们的使用,但为了完整性,这里是如何进行同步呼叫:

没有 jQuery

jQuery

function foo() {
    var jqXHR = $.ajax({
        //...
        async: false
    });
    return jqXHR.responseText;
}

如果您使用任何其他 jQuery Ajax 方法,如 $.get, $.getJSON 等,您必须将其更改为 $.ajax (因为您只能将配置参数转移到 $.ajax)。

你的代码应该是沿着这条线的一点:

function foo() {
    var data;
    // Or $.get(...).then, or request(...).then, or query(...).then
    fetch("/echo/json").then(function(response){
        data = response.json();
    });
    return data;
}

var result = foo(); // 'result' is always undefined no matter what.

---

当我们打电话给一个承诺并从中返回一些东西时,我们会得到处理的价值的承诺;如果我们返回另一个承诺,我们会得到惊人的东西,但让我们抓住我们的马。

function delay(ms){ // Takes amount of milliseconds
    // Returns a new promise
    return new Promise(function(resolve, reject){
        setTimeout(function(){ // When the time is up,
            resolve(); // change the promise to the fulfilled state
        }, ms);
    });
}

基本上,而不是返回一个值,我们不能因为竞争模式 - 我们正在返回一个值,我们可以与它无缝。

function foo() {
    // RETURN the promise
    return fetch("/echo/json").then(function(response){
        return response.json(); // Process it inside the `then`
    });
}

foo().then(function(response){
    // Access the value inside the `then`
})

function* foo(){ // Notice the star. This is ES6, so new browsers, Nodes.js, and io.js only
    yield 1;
    yield 2;
    while(true) yield 3;
}

var foo = coroutine(function*(){
    var data = yield fetch("/echo/json"); // Notice the yield
    // The code here only executes _after_ the request is done
    return data.json(); // 'data' is defined
});

var main = coroutine(function*(){
   var bar = yield foo(); // Wait our earlier coroutine. It returns a promise
   // The server call is done here, and the code below executes when done
   var baz = yield fetch("/api/users/" + bar.userid); // Depends on foo's result
   console.log(baz); // Runs after both requests are done
});
main();

2016年(ES7)

在ES7中,这一点进一步标准化了,现在有几个建议,但在所有这些建议中,你可以等待承诺,这只是ES6提议的“糖”(尼克合成)通过添加同步并等待关键词。

async function foo(){
    var data = await fetch("/echo/json"); // Notice the await
    // code here only executes _after_ the request is done
    return data.json(); // 'data' is defined
}

下面我写的例子表明如何

处理无同步的 HTTP 通话; 等待每个 API 通话的响应; 使用 Promise 模式; 使用 Promise.all 模式加入多个 HTTP 通话;

[
 "search?type=playlist&q=%22doom%20metal%22",
 "search?type=playlist&q=Adele"
]

对于每个项目,一个新的承诺将燃烧一个区块 - ExecutionBlock,打破结果,根据结果序列安排一个新的承诺集,这是 Spotify 用户对象的列表,并在 ExecutionProfileBlock 中无同步执行新的 HTTP 通话。

然后,你可以看到一个被遗弃的承诺结构,允许你扫描多个和完全无同步的遗弃的HTTP通话,并通过 Promise.all 加入每个子组的通话的结果。

-H "Authorization: Bearer {your access token}" 

我在这里讨论了这个解决方案。

答案简短的是,你必须执行这样的呼叫回复:

function callback(response) {
    // Here you can do what ever you want with the response object.
    console.log(response);
}

$.ajax({
    url: "...",
    success: callback
});

标签: 假

我通过将 async 设置为虚假,并重组我的 Ajax 呼叫:

我设置了一个全球性函数,称为 sendRequest(类型,URL,数据),有三个参数,每次在任何地方都会被召唤:

function sendRequest(type, url, data) {
    let returnValue = null;
    $.ajax({
        url: url,
        type: type,
        async: false,
        data: data,
        dataType: 'json',
        success: function (resp) {
            returnValue = resp;
        }
    });
    return returnValue;
}

接下来的函数:

let password = $("#password").val();
        let email = $("#email").val();
        let data = {
            email: email,
            password: password,
        };
        let  resp =  sendRequest('POST', 'http://localhost/signin')}}", data);
        console.log(resp);

此分類上一篇: async: false

如果这个解决方案不与您合作,请注意,这可能不会在某些浏览器或jQuery版本工作。

urls = ['https://jsonplaceholder.typicode.com/todos/2',
        'https://jsonplaceholder.typicode.com/todos/3']

{"userId":1,"id":2,"title":"quis ut nam facilis et officia qui",
 "completed":false}
{"userId":1,"id":3,"title":"fugiat veniam minus","completed":false}

namesonly = ['two', 'three']

[{"name":"two","loremipsum":"quis ut nam facilis et officia qui"},
{"name":"three","loremipsum":"fugiat veniam minus"}]

...
  "release-groups": [
    {
      "id": "1dc4c347-a1db-32aa-b14f-bc9cc507b843",
      "secondary-type-ids": [],
      "first-release-date": "2000-07-10",
      "primary-type-id": "f529b476-6e62-324f-b0aa-1f3e33d313fc",
      "disambiguation": "",
      "secondary-types": [],
      "title": "Parachutes",
      "primary-type": "Album"
    },
...

此 JSON 剪辑显示 Coldplay 的第一张专辑是 Parachutes. 它还提供了一个 ID,在这种情况下 1dc4c347-a1db-32aa-b14f-bc9cc507b843,这是专辑的独特标识。

对于每个专辑,JSON答案包含一些图像,其中一个是专辑的前面覆盖。

{
  "images": [
    {
      "approved": true,
      "back": false,
      "comment": "",
      "edit": 22132705,
      "front": true,
      "id": 4086974851,
      "image": "http://coverartarchive.org/release/435fc965-9121-461e-b8da-d9b505c9dc9b/4086974851.jpg",
      "thumbnails": {
        "250": "http://coverartarchive.org/release/435fc965-9121-461e-b8da-d9b505c9dc9b/4086974851-250.jpg",
        "500": "http://coverartarchive.org/release/435fc965-9121-461e-b8da-d9b505c9dc9b/4086974851-500.jpg",
        "1200": "http://coverartarchive.org/release/435fc965-9121-461e-b8da-d9b505c9dc9b/4086974851-1200.jpg",
        "large": "http://coverartarchive.org/release/435fc965-9121-461e-b8da-d9b505c9dc9b/4086974851-500.jpg",
= = >   "small": "http://coverartarchive.org/release/435fc965-9121-461e-b8da-d9b505c9dc9b/4086974851-250.jpg"
    },
...

这里有兴趣的是“小”的线:“http://coverartarchive.org/release/435fc965-9121-461e-b8da-d9b505c9dc9b/4086974851-250.jpg”。

创建和视觉化Mashup的代码

const lock = setTimeout(() => {}, 43210);
const albumsArray = [];
const urlsArray = [];
const urlOuter = 'https://musicbrainz.org/ws/2/artist/' +
  pm.collectionVariables.get('MBID') + '?fmt=json&inc=url-rels+release-groups';
pm.sendRequest(urlOuter, (_, responseO) => {
  const bandName = responseO.json().name;
  const albums = responseO.json()['release-groups'];
  for (const item of albums) {
    albumsArray.push(item.title);
    urlsArray.push('https://coverartarchive.org/release-group/' + item.id);
  }
  albumsArray.length = urlsArray.length = 15;
  const images = [];
  let countDown = urlsArray.length;
  urlsArray.forEach((url, index) => {
    asynchronousCall(url, imageURL => {
      images[index] = imageURL;
      if (--countDown === 0) { // Callback for ALL starts on next line.
        clearTimeout(lock); // Unlock the timeout.
        const albumTitles = albumsArray.map(value => ({ title: value }));
        const albumImages = images.map(value => ({ image: value }));
        const albumsAndImages = albumTitles.map(
          (item, i) => Object.assign({}, item, albumImages[i]));
        const template = `<table>
          <tr><th>` + bandName + `</th></tr>
          {{#each responseI}}
          <tr><td>{{title}}<br><img src="{{image}}"></td></tr>
          {{/each}}
        </table>`;
        pm.visualizer.set(template, { responseI: albumsAndImages });
      }
    });
  });
  function asynchronousCall (url, callback) {
    pm.sendRequest(url, (_, responseI) => {
      callback(responseI.json().images.find(obj => obj.front === true)
        .thumbnails.small); // Individual callback.
    });
  }
});

结果和文档

此分類上一篇

---