JavaScript while loop + setInterval doesn't work in Django

Question

I'm developing a website using Django. I have about 50 functions. And it takes about 1 minute to get the result for all of them.

The problem is that I use heroku for my app. And heroku has a limit of 30 sec to get the request. I was suggested to use background tasks. Now I am using background jobs in Python RQ. For each function I made a separate task in Views. Here is an example of one of the tasks:

task_robots_url = q.enqueue(Robots(url).get_url)
robots_url = task_robots_url.result

And now I need to check whether the job is finished in the Template. And when it's finished, display the result.

I want to check with JS each second whether the job is finished. If it's not finished - show "Loading ... " message to the user. If it's finished - show the result.

Here is my JS code:

  <script>
    var h1 = document.getElementById("h1");
    var job_result = "{{ robots_url }}"

    var test = function () {
      if (job_result ==  "") {
          h1.innerText = "Waiting...";
          } else if (job_result == "None") {
          h1.innerText = "Waiting ...";
          } else if (job_result == undefined) {
          h1.innerText = "Waiting ...";
          } else { 
          clearInterval(inter);
          h1.innerText = job_result; 
          }
      }
    var inter = setInterval(test, 1000);
  </script>

But this doesn't work. When the result page starts - I've got an empty result. And it displays Waiting. Then I have None result. And it still displays Waiting. But now after waiting there is no result.

In the documentation for Python RQ it is said I should put time.sleep() for several seconds in my code. And if I put time.sleep(2) - I got the result. But if I put time.sleep(2) for each of my 50 functions - I will get 100 sec. And the limit in Heroku is only 30 sec... So I need to check and display the result without sleep()...

Barak Avraham · Accepted Answer · 2020-06-20T17:24:31.833

1

The setInterval() method calls a function or evaluates an expression at specified intervals (in milliseconds).

The setInterval() method will continue calling the function until clearInterval() is called, or the window is closed.

You are calling setInterval so many times which cause your browser to crash eventually.

assuming job_result value changes after 10 sec you can write the following code:

var job_result = {{ job_result }};

var loadingMessage = function (){
    if (!job_result) {
        document.write("Loading ...");
    }
    else {
        return
    }
}

setInterval(() => loadingMessage, 1000);

You can call return to stop the Interval for running or you can use setTimeout and to call a function that clears the interval

edited Jun 20 '20 at 17:24

answered Jun 20 '20 at 17:10

Barak Avraham

96
2

Thank your for your answer. I've edited my JS. But I still have no result. Can you suggest anything else? I also edited the description of my problem - added more details – djangodjames Jun 21 '20 at 12:12
@djangodjames sounds like you have an issue with your code in python, how you detects when job_result is complete? what task_robots_url.result gives you? – Barak Avraham Jun 21 '20 at 12:56
If I try task_robots_url.result instead of robots_url in the same javascript. It returns the following: ``` <Job 0071bc00-32ad-4ab5-8975-275258806f57: get_url()> ``` – djangodjames Jun 23 '20 at 09:53

JavaScript while loop + setInterval doesn't work in Django

1 Answers1