异步延迟JS直到满足条件

Question

我有一个类,ChatRoom它只能在收到长时间运行的HTTP请求后呈现(可能需要1秒或30秒).所以我需要延迟渲染,直到ChatRoom.json不为空.

在下面的代码中,我正在使用Closure Library goog.async.ConditionalDelay.它有效,但是有更好的方法(可能不需要Closure Library)吗？

ChatRoom.prototype.json = null; // received after a long-running HTTP request.

ChatRoom.prototype.render = function() {
    var thisChatRoom = this;

    function onReady() {
        console.log("Received JSON", thisChatRoom.json);
        // Do rendering...
    }

    function onFailure() {
        alert('Sorry, an error occurred. The chat room couldn\'t open');
    }

    function isReady() {
        if (thisChatRoom.json != null) {
            return true;
        }
        console.log("Waiting for chat room JSON...");
        return false;
    }

    // If there is a JSON request in progress, wait until it completes.
    if (isReady()) {
        onReady();
    } else {
        var delay = new goog.async.ConditionalDelay(isReady);
        delay.onSuccess = onReady;
        delay.onFailure = onFailure;
        delay.start(500, 5000);
    }
}

请注意,"while(json == null){}"是不可能的,因为这将是同步的(阻止所有其他JS执行).

Answer 1

考虑一下:

(function wait() {
    if ( chatroom.json ) {
        chatroom.render();
    } else {
        setTimeout( wait, 500 );
    }
})();

这将每半秒检查一次.

现场演示: http ://jsfiddle.net/kBgTx/