javascript – 没有UI块的处理函数链

我需要在我的JavaScript / jQuery中执行几个函数,但我想避免阻止UI.

AJAX不是一个可行的解决方案,因为应用程序的性质,这些功能将很容易达到成千上万.异步执行此操作会终止浏览器.

因此,我需要某种方式来链接浏览器需要处理的函数,并且只在第一个函数完成后发送下一个函数.

算法是这样的

For steps from 2 to 15

HTTP:GET amount of items for current step (ranges somewhere from a couple of hundred to multiple thousands)

For every item, HTTP:GET the results

  

如你所见,我有两个GET请求 – “链”我不知何故需要管理…尤其是最里面的循环立即崩溃浏览器,如果它是异步完成的 – 但我仍然希望用户能够操作页面,因此纯(阻塞)同步方式不起作用.

解决方法:

您可以轻松地异步执行此操作,而无需立即触发所有请求.您需要做的就是管理队列.为清楚起见,以下是伪代码.它很容易转换为真正的AJAX请求：

// Basic structure of the request queue. It's a list of objects
// that defines ajax requests:
var request_queue = [{
    url : "some/path",
    callback : function_to_process_the_data
}];

// This function implements the main loop.
// It looks recursive but is not because each function
// call happens in an event handler:
function process_request_queue () {
    // If we have anything in the queue, do an ajax call.
    // Otherwise do nothing and let the loop end.
    if (request_queue.length) {
        // Get one request from the queue. We can either
        // shift or pop depending on weather you prefer
        // depth first or breadth first processing:
        var req = request_queue.pop();
        ajax(req.url,function(result){
            req.callback(result);
            // At the end of the ajax request process
            // the queue again:
            process_request_queue();
        }
    }
}

// Now get the ball rolling:
process_request_queue();

所以基本上我们将ajax调用本身转换为伪循环.它基本上是递归传递的经典延续传递方式.

在您的情况下,请求的示例将是：

request_queue.push({
    url : "path/to/OUTER/request",
    callback : function (result) {
        // You mentioned that the result of the OUTER request
        // should trigger another round of INNER requests.
        // To do this simply add the INNER requests to the queue:

        request_queue.push({
            url : result.inner_url,
            callback : function_to_handle_inner_request
        });
    }
});

这非常灵活,因为您不仅可以选择先处理广度,还可以先处理深度(shift与pop).但是你也可以使用splice将东西添加到队列的中间,或者使用unshift vs push将请求放在队列的头部以获得高优先级请求.

您还可以通过为每个循环弹出多个请求来增加同时请求的数量.只需确保每个循环只调用一次process_request_queue,以避免同时发生请求的指数级增长：

// Handling two simultaneous request channels:
function process_request_queue () {
    if (request_queue.length) {
        var req = request_queue.pop();
        ajax(req.url,function(result){
            req.callback(result);
            // Best to loop on the first request.
            // The second request below may never fire
            // if the queue runs out of requests.
            process_request_queue();
        }
    }
    if (request_queue.length) {
        var req = request_queue.pop();
        ajax(req.url,function(result){
            req.callback(result);
            // DON'T CALL process_request_queue here
            // We only want to call it once per "loop"
            // otherwise the "loop" would grow into a "tree"
        }
    }
}