javascript - 试图让 knockout js 检查数据是否每 10 秒来一次

Question

我正在尝试调用发布 ajax 请求的函数来检查数据库，每 10 秒查看我想要的所需信息是否已到达，如果所需信息在 60 秒内未到达，我只想退出功能。我现在遇到的问题是，我的函数没有每 10 秒调用一次 self.startInstantorCheck，然后在 60 秒后退出到最后。这是函数

self.startInstatorCheck = function(){
                self.instatorStarts(true);
                var MAX_WAIT_TIME_MS = 1 * 60 * 1000;
                var POST_INTERVAL_MS = 10 * 1000;
                var timeoutTime = null;
                $.ajax({
                       type: 'POST',
                       url: BASEURL + 'index.php/moneyexchange/check_instantor_field/' + auth,
                      contentType: 'application/json; charset=utf-8'
                   })
                .done(function(userinfo) {
                    if (timeoutTime == null) {
                      // Start of the timeout cycle:
                      timeoutTime = Date.now() + MAX_WAIT_TIME_MS;
                    }
                    if (userinfo.instantor_request > 12) {
                      self.allInstantorCheckMessages('Instantor data gathered');
                    } else {
                      if (Date.now() < MAX_WAIT_TIME_MS) {
                        setTimeout(self.startInstatorCheck(), POST_INTERVAL_MS);
                      } else {
                          self.allInstantorCheckMessages('Please go through instantor to ');
                          self.instatorStarts(true);
                          self.magicInstantorbtn2(true);
                      }
                    }
                 })
               .fail(function(jqXHR, textStatus, errorThrown) {
                   self.errorMessage(errorThrown);
               })
               .always(function(data){               
               });
        }
I am using knockout js, so would be great if the answers or help are related to knockout js. 

Answer 1

首先，这里简化了您的代码以减少嵌套并通过命名提供清晰度。

           self.startInstatorCheck = function(){
                self.instatorStarts(true);
                var MAX_WAIT_TIME_MS = 1 * 60 * 1000;
                var POST_INTERVAL_MS = 10 * 1000;
                var timeoutTime = null;
                $.ajax({
                       type: 'POST',
                       url: BASEURL + 'index.php/moneyexchange/check_instantor_field/' + auth,
                      contentType: 'application/json; charset=utf-8'
                   })
                .done(function(userinfo) {
                    // please use === not == 
                    // == doesn't always do what you want it to do, NEVER use it
                    timeoutTime = timeoutTime === null ?  
                        Date.now() + MAX_WAIT_TIME_MS :
                        timeoutTime;

                    var pleaseNameMe = userinfo.instantor_request > 12
                    if (pleaseNameMe) {
                      return self.allInstantorCheckMessages('Instantor data gathered');
                    }

                    var expired = Date.now() < MAX_WAIT_TIME_MS
                    if (!expired) {
                      return setTimeout(self.startInstatorCheck(), POST_INTERVAL_MS);
                    }

                    self.allInstantorCheckMessages('Please go through instantor to ');
                    self.instatorStarts(true);
                    self.magicInstantorbtn2(true);

               })
               .fail(function(jqXHR, textStatus, errorThrown) {
                   self.errorMessage(errorThrown);
               })
               .always(function(data){               
               });
        }

其次，你的问题之前已经解决了，knockoutjs与否。 Here is a wonderful article这解释了如何使用超时在 javascript 中进行轮询。它建议使用 promise 。我非常同意。 (它们可以而且应该与 knockout js 结合使用。)直接来自博客的人为示例:

// The polling function
function poll(fn, timeout, interval) {
    var dfd = new Deferred();
    var endTime = Number(new Date()) + (timeout || 2000);
    interval = interval || 100;

    (function p() {
            // If the condition is met, we're done! 
            if(fn()) {
                dfd.resolve();
            }
            // If the condition isn't met but the timeout hasn't elapsed, go again
            else if (Number(new Date()) < endTime) {
                setTimeout(p, interval);
            }
            // Didn't match and too much time, reject!
            else {
                dfd.reject(new Error('timed out for ' + fn + ': ' + arguments));
            }
    })();

    return dfd.promise;
}

// Usage:  ensure element is visible
poll(function() {
    return document.getElementById('lightbox').offsetWidth > 0;
}, 2000, 150);