<style>

    div {

        width: 50px;

        height: 50px;

        background-color: green;

    }

    div.square {

        width: 100px;

        height: 100px;

        -webkit-transition-property: height;

        -webkit-transition-duration: 2s;

    }

    div.rectangle {

        width: 100px;

        height: 200px;

        -webkit-transition-property: width, height;

        -webkit-transition-duration: 5s;

    }

</style>

<p id="instructions">

    When you click the Change button, the shape will

    <span id="description"></span>.

    <button style="display: block;" onclick="transition()">Change</button>

</p>

<div id="target"></div>

<script>

    var state = 0;

    var transitions = [

        {className:"rectangle", description:"animate to a large rectangle over 5 seconds."},

        {className:"square", description:"animate to a square over 2 seconds.  Try clicking before the first animation finishes and make sure the width doesn't do an ugly jump."},

        {className:"", description:"instantly change to a small square"},

        {className:"square", description:"instantly change into a small rectangle and then animate into a large square over 2 seconds"},

        {className:"rectangle", description:"animate to a large rectangle over 5 seconds"},

        {className:"", description:"instantly change to a small square"}

    ];

    document.getElementById("description").innerText = transitions[0].description;

    function transition()

    {

        var target = document.getElementById("target");

        target.className = transitions[state].className;

        state++;

        if (state < transitions.length)

            document.getElementById("description").innerText = transitions[state].description;

        else {

            document.getElementById("instructions").innerText = "Done.";

        }

    }

</script>