javascript - 异步推送数组中的项目

Question

我想将一个对象插入数组，其中一个字段是需要从异步函数获取的值

function loadContentAsync(url) {
    var deferred = Q.defer();
    request(url, function (err, res, html) {
        if (!err) {
            deffered.resolve(html);
        }
    });
    return deffered.promise;
}

var aList = $('#mCSB_5_container ul').find('a');
console.log(c);

var list = [];
aList.each(function (i, elem) {
    var html = loadContentAsync(this.attribs.href);
    list.push({
        title: $(this).text(),
        url: this.attribs.href,
        content: html
    });
});

但是当我运行此代码时，由于 loadContentAsync 函数没有同步返回值，因此 html 字段将为 null。

如何异步处理该字段？

Answer 1

您需要等待 promise 得到解决。为了保持元素的正确顺序，您应该使用 Q.all() 来累积所有 Promise 的结果:

function loadContentAsync(url) {
    var defer = Q.defer();
    request(url, function (err, res, html) {
        if (err) {
            defer.reject(err);
        }
        else {
            defer.resolve(html);
        }
    });
    return defer.promise;
}

var aList = $('#mCSB_5_container ul').find('a');
console.log(c);

var promises = aList.map(function (i, elem) {
    return loadContentAsync(this.attribs.href);
}).get();

var list = [];
Q.all(promises).then(function (htmlList) {
    htmlList.forEach(function (html) {
        list.push({
            title: $(this).text(),
            url: this.attribs.href,
            content: html
        });
    });
});