如何使用javascript onclick事件调用php函数？

image onclick using javascript and javacript function is used to call the php function. How to call php function using javascript on click event and the php is on the same page.

<input type="image" src="test.png" height="45" width="45" onclick="clickCall()" align="right"/>

<script type="text/javascript">
function clickCall(){
    var phpcall=<?php saveCallClickUsage(); ?>    
}
</script>

<?php 
function saveCallClickUsage(){
    echo "<script>alert('test');</script>";
}
?>

Use Ajax for do that. Hope it helpful.