javascript - setTimeout 尝试等待异步执行的问题

Question

我对 JavaScript 中的此类问题很陌生，我无法修复此等待结合 Angular Promise 对象和超时的异步调用的尝试。

函数 onTimeout 似乎永远不会执行。

getAsyncContent: function (asyncContentInfos) {

    var deferObj = $q.defer();
    var promiseObj = deferObj.promise;
    asyncContentInfos.promiseObject = promiseObj;
    var blockingGuard = { done: false };

    promiseObj.then(function () {
        blockingGuard.done = true;
    });

    this.wait = function () {
        var executing = false;
        var onTimeout = function () {
            console.log("******************** timeout reached ********************");
            executing = false;
        };

        while (!blockingGuard.done) {
            if (!executing && !blockingGuard.done) {
                executing = true;
                setTimeout(onTimeout, 200);
            }
        } 
    };

    $http.get(asyncContentInfos.URL, { cache: true })
        .then(function (response) {
            asyncContentInfos.responseData = response.data;
            console.log("(getAsyncContent) asyncContentInfos.responseData (segue object)");
            console.log(asyncContentInfos.responseData);
            deferObj.resolve('(getAsyncContent) resolve');
            blockingGuard.done = true;
            return /*deferObj.promise*/ /*response.data*/;
        }, function (errResponse) {
            var err_msg = '(getAsyncContent) ERROR - ' + errResponse;
            deferObj.reject(err_msg);
            console.error(err_msg);
        });

    return {
        wait: this.wait
    }
}

客户端代码是这样的:

var asyncVocabulary = new AsyncContentInfos(BASE_URL + 'taxonomy_vocabulary.json');
getAsyncContent(asyncVocabulary).wait();

AsyncContentInfos 是:

function AsyncContentInfos(URL) {
    this.URL = URL;
    this.responseData = [];
    this.promiseObject;
    }

Answer 1

$http.get 返回一个 promise ，该 promise 将在调用完成时解析。 Promise 是一种使异步比普通的旧回调更干净、更直线的方法。

getAsyncContent: function (asyncContentInfos) {

    return $http.get(asyncContentInfos.URL, { cache: true })
        .then(function (response) {
            return response.data;
        }, function (errResponse) {
            console.error(err_msg);
            throw errResponse;
        });
}

然后使用它:

getAsyncContent({...}).then(function(yourDataIsHere) {

});

Promise 的好处是它们可以轻松链接。

getAsyncContent({...})
  .then(function(yourDataIsHere) {
     return anotherAsyncCall(yourDataIsHere);
  })
  .then(function(your2ndDataIsHere) {
  });