It seems Jacob Gray has provided a solid answer, but I have an alternative suggestion:
Check out this Fiddle
This method utilizes css for the animation rather than relying on javascript. JavaScript is only used to initiate the animation, while the bulk of it is handled by css.
The key aspect here is using the css transition property to create a "animation" effect as the height transitions from 100% to 0%. One significant change in the html is swapping the background of the inner and outer elements.
This solution may prove more suitable for some readers of this thread depending on their specific implementation and preferences.
$(document).ready(function() {
$('#inner-progress').addClass("load");
});
#outer-progress {
background-image: url(https://www.novilar.com/img/battle/ui/purification_meter_bar.png);
background-color: transparent;
border: 0;
height: 100px;
width: 100px;
position: relative;
}
#inner-progress {
background-image: url(https://www.novilar.com/img/battle/ui/purification_meter_background.png);
background-color: transparent;
width: 100%;
overflow: hidden;
position: relative;
bottom: 0;
height: 100%;
transition: height 3s;
-webkit-transition: height 3s;
}
.progress-value {
color: #FFF !important;
font-weight: bold;
position: absolute;
top: 40%;
left: 40%;
}
.load{
height: 0% !important;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<div id="outer-progress">
<div id="inner-progress" value="0" max="100"></div>
<span class="progress-value">0%</span>
</div>