Question

我正在检测一个值是否已经存储在localStorage中（如果localStorage存在），如果它不在数据库中（或者用户没有带有localStorage的浏览器），那么我运行一个AJAX GET请求。

if (Modernizr.localstorage) {
    // there is storage
    artist = localStorage.getItem('artist');
    if (!artist) {
        // but no cache
        artist = fetchArtist();
        localStorage.setItem('artist', artist)
    }
} else {
    // there's no storage
    artist = fetchArtist();
}
function fetchArtist() {
    var fetchedArtist;
    var recentTracks;
    $.get('script.php', [], function(data) {
        recentTracks = data.recenttracks;
        fetchedArtist = ((recentTracks !== undefined) ? recentTracks.track.artist['#text'] : 'Last.fm connection failed.');
    }, 'json');
    return fetchedArtist;
}

script.php只获取一个JSON字符串，jQuery将其转换为数据对象。我可以看到问题：因为$ .get是异步的，所以在函数可以分配我之后的值之前返回fetchedArtist变量，但是我想不出这样做的一种整洁方式（也许是全局变量，但是我真的不愿意。我可以在console.log中获取 $ .get中的fetchedArtist var 和我之后的值，但是fetchArtist函数总是返回undefined。

Answer 1

您必须通过从fetchArtist()函数中删除return语句来异步化您的工作流，因为$.get请求的异步行为导致它无法满足您的需求。

尝试这样的事情：


if (Modernizr.localstorage) {
    // there is storage
    var artist = localStorage.getItem('artist');
    if (!artist) {
        // but no cache
        fetchArtist();
    } else {
        doWhatYouNeedWithArtist( artist );
    }
} else {
    // there's no storage
    fetchArtist();
}

function fetchArtist() {
    var fetchedArtist;
    var recentTracks;
    $.get('script.php', [], function(data) {
        recentTracks = data.recenttracks;
        fetchedArtist = ((recentTracks !== undefined) ? recentTracks.track.artist['#text'] : 'Last.fm connection failed.');
        if ( Modernizr.localstorage ) {
                Modernizr.localstorage.setItem('artist', fetchedArtist);
        }
        // then do your stuff
        doWhatYouNeedWithArtist( fetchedArtist );
    }, 'json');
}

function doWhatYouNeedWithArtist( artists ) {
    // do stuff
}

希望这有帮助！侨

变量拒绝在jQuery.get回调函数中获取值

1 个答案: