JS <（小于）运算符失败

I have a script that AJAXes a request every 10 seconds (but technically 11), for the user. I have a simple countdown made from 10 to 0 and then again and again.

This countit function is called after each AJAX request to restart

Here is my code:

function countit() {
  var count = 10;
  loading = setInterval(function() {
    $(box).val("Will automatically check in " + count + "second(s), please DO NOT refresh the page yourself.");
    count--;
    if (count <= 0) {
      clearInterval(loading);
    }

  }, 1000);
}

The code works fine except, if you leave the page and come back, the countdown proceeds into negative and does not stop. Here is the image:

I cant be sure if this is a problem with the code or JS but the counter doesnt go below 0 when the user stays on the page.

As Ibrahim & Chris have said:

Add a var infront of the Interval as without it, the variable is global.

function countit() {
    var count = 10;
    var loading = setInterval(function() {
        $(box).val("Will automatically check in " + count + "second(s), please DO NOT refresh the page yourself.");
        count--;
        if (count <= 0) {
            clearInterval(loading);
        }
    }, 1000);
}