I am using Apex command button to perform certain operation. after completion of the operation I want to display certain message in popup window. 

Can somebody help me on this.

```
<apex:commandButton action="(method name)" 
                    id="<id value>" 
                    oncomplete="showPopUp" 
                    value="<test>" 
                    style="margin-left: 20px;" 
                    rendered="<rendering logic>" />
<script> 
    function showPopUp() { alert("Need to Populate publication Type"); } 
</script>

```