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)。
