回调，承诺，异步在Javascript中等待-仍然令人困惑 [英] Callbacks, Promises, Async await in Javascript - still confusing
问题描述
我是Java语言的新手，我看到了很多视频，但我仍然无法理解回调，promise和async等待的确切用法。
I am new to Javascript, i see lot of videos, still i cant understand this exact use of callbacks, promises and async await. Here i write small code upto my knowlege.
我的index.html：
My index.html:
<!DOCTYPE html>
<html lang="en" ng-app='myApp'>
<head>
<meta charset="UTF-8">
<title>Index</title>
<script src='https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.6.5/angular.min.js'></script>
<script src='https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js'></script>
<script src='script.js'></script>
</head>
<body ng-controller='myController'>
</body>
</html>
script.js：
angular
.module('myApp', [])
.controller('myController', function($scope, $http) {
// i think these are callbacks
function callback(response) {
console.log("Animal name:", response.data);
}
function callbackerr(response) {
console.log("err:", response);
}
$http({
method: 'GET',
url: 'animalname.json'
}).then(callback)
.catch(callbackerr);
// i think these are promises
$http({
method: 'GET',
url: 'animalage.json'
}).then(function(response) {
console.log("Animal age: ", response.data);
}).catch(function(error) {
console.log(error);
})
// i think to write new code in async await
// how to write my above code using async await?
});
如果我对回调的假设是错误的，请修改并解释。
Please modify and explain, if my assumption about callbacks,promises is wrong.
帮帮我！
推荐答案
回调只是一个函数，它作为参数传递给另一个函数，然后在其中执行。一个promise只是一个也接受回调的模式。要在javascript中使用新的异步/等待模式编写相同内容，您可以编写如下内容。
A callback is simply a function that is passed as an argument into another function and then executed within. A promise is just a pattern that also accepts callbacks. To write the same thing using the new async/await pattern in javascript you could write something like this.
请注意，控制器函数的前缀为async。
Note the controller function is prefixed with async.
异步/等待只会使代码看起来更具程序性。
Async/await just makes the code look more procedural.
angular
.module('myApp', [])
.controller('myController', async function($scope, $http) {
const response = await $http({
method: 'GET',
url: 'animalage.json'
})
console.log("Animal age: ", response.data);
});
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