Full code after the jump.

View MXML

<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2007/10/11/changing-the-default-easing-function-on-a-wipe-effect/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white">

    <mx:Script>
        <![CDATA[
            import mx.effects.easing.*;
        ]]>
    </mx:Script>

    <mx:WipeLeft id="wipeLeft"
            target="{image}"
            moveEasingFunction="Elastic.easeOut"
            duration="5000" />

    <mx:ApplicationControlBar dock="true">
        <mx:Button label="Start wipe"
                click="wipeLeft.play();" />
    </mx:ApplicationControlBar>

    <mx:Image id="image"
            source="assets/flex_sm.png" />

</mx:Application>

View source is enabled in the following example.