onsubmit : how to get submit button clicked on Safari?

Question

I have a form with 2 submit buttons. On the form tag, I put onsubmit="return foo();"

So when I click in one of the two submit buttons, I can retrieve the submit element thanks to document.activeElement in IE, Chrome, Firefox. But document.activeElement doesn't work in safari (document.activeElement return a body element instead of the submit button element).

Here my code (you can try it at https://jsfiddle.net/m6quo8rs/ ) :

<form onsubmit="foo();">

<input type="submit" id="submit_button_1" value="Submit button 1">
<input type="submit" id="submit_button_2" value="Submit button 2">

</form> 

<script type="text/javascript">

function foo()
{
    //Retrieve the submit button clicked thanks to document.activeElement :

    console.log(document.activeElement);
}

</script>

This code works in IE, Chrome, Firefox, but doesn't work in Safari.

Have you a solution for safari ?