Tryit Editor v2.9

Edit This Code:
<!DOCTYPE html>
<html>
<head>
<style>
#myDiv {
    border: 1px solid red;
    outline: dotted green;
}
</style>
</head>
<body>

<div id="myDiv" style="outline-width:10px;">This is a div element.</div>
<br>
<button type="button" onclick="myFunction()">Return outline width</button>

<script>
function myFunction() {
    alert(document.getElementById("myDiv").style.outlineWidth);
}
</script>

</body>
</html>