Run php function on button click

Question

I want to run a php function on button click. for eg :

<input type="button" name="test" id="test" value="RUN"  onclick="<?php echo testfun(); ?>" /><br/>

<?php

function testfun()
{
   echo "Your test function on button click is working";
}

?>

My question is that when I do this I don't get the expected output I was looking for. Please give me the best solution for this to run a php function on button click whether it is a simple button or submit.

Answer 1

I tried the code of William, Thanks brother.

but it's not working as a simple button I have to add form with method="post". Also I have to write submit instead of button.

here is my code below..

<form method="post">
    <input type="submit" name="test" id="test" value="RUN" /><br/>
</form>

<?php

function testfun()
{
   echo "Your test function on button click is working";
}

if(array_key_exists('test',$_POST)){
   testfun();
}

?>