异步延迟JS直到满足条件 [英] Asynchronously delay JS until a condition is met

问题描述

我有一个类ChatRoom，该类只能在接收到长时间运行的HTTP请求后才能呈现(可能需要1秒或30秒).因此，我需要延迟渲染，直到ChatRoom.json不为空.

I have a class, ChatRoom, that can only render after it receives a long-running HTTP request (it could take 1 second or 30 seconds). So I need to delay rendering until ChatRoom.json is not null.

在下面的代码中，我正在使用Closure Library的

In the code below, I'm using Closure Library's goog.async.ConditionalDelay. It works, but is there a better way (maybe without needing Closure Library) to do this?

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).

Note that "while (json == null) { }" isn't possible because that would be synchronous (blocking all other JS execution).

推荐答案

请考虑以下问题:

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

这将每半秒检查一次.

实时演示: http://jsfiddle.net/kBgTx/

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