How to get drop down value when drop down change using javascript

Here is the sample example to the get value from the drop down

Select Black Select Red Select Blue Select Green

 Here the code is 

<script>
function changeFunction(){
	var color = document.getElementById('color').value;
	alert(color);
}
</script>
<select onchange="changeFunction()" id="color">
<option value="black">Select Black</option>
<option value="red">Select Red</option>
<option value="blue">Select Blue</option>
<option value="green">Select Green</option>
</select>