title: Slide Up Linear Easing First Step Does Nothing
body: <p>I'm developing an accordion plugin, and it's mostly done except for one bug where for the first few steps of the slideUp/slideDown, the accordion is 1px taller than it's meant to be, causing a visual bug. I've narrowed it down to the fact that the first step in the slideUp animation doesn't do anything, and I can't figure out why. Here's an example:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>console.log('Start');
  var diff = 0;
  var upNow = 100;
  var downNow = 0;
  $.fx.interval = 1000;
  var duration = $.fx.interval * 100;
  $("#div1").slideUp({
    easing: 'linear',
    duration: duration,
    step: function(now) {
      if (now != 0 &amp;&amp; now &gt; 90) {
        console.log("Slide Up: " + now);
        upNow = now;
      }
    }
  });
  
  $("#div2").slideDown({
    easing: 'linear',
    duration: duration,
    step: function(now) {
      if (now != 0 &amp;&amp; now &lt; 10) {
        downNow = now;
        diff = 100 - (upNow + downNow);
        console.log("Slide Down: " + now);
        console.log("Slide Difference:" + diff);
      }
    }
  });</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"&gt;&lt;/script&gt;
  &lt;div style='height: 100px; background-color: red;' id='div1'&gt;
  &lt;/div&gt;
  
  &lt;div style='height: 100px; background-color: blue; display: none;' id='div2'&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p><a href="http://jsfiddle.net/hbh6U/" rel="nofollow noreferrer">http://jsfiddle.net/hbh6U/</a></p>
  
  <p>The problem is that I need these to be in sync, and I can't figure out why they're not, or how to get them in sync. One idea I've had is to skip the first step of the <code>slideDown</code> animation, but I'm not sure how to do that either. Has anyone got any ideas, or faced this bug before?</p>