Enable/disable button based on accepting the 2 checkbox conditions

I have gone through the stackoverflow regarding enable/disable button conditionally and was able to find some help but NOT EXACT what I was looking for.

Instead of 1 checkbox condition, I have 2 checkbox conditions. So unless if the two checkboxes have been accepted, the button should not be enabled.

Following is my html:

<input type="checkbox" id="f_agree" value="1" onchange="checked(this, 'f_agree2')"/>
<input type="checkbox" id="f_agree2" value="1" onchange="checked('f_agree', this)"/>

Following is javascript:

function checked(element1, element2) {
    var myLayer = document.getElementById('acceptbtn');

   if (element1.checked == true && element2.checked == true) {
        myLayer.class = "submit";
        myLayer.disabled = "";
   } else {
        myLayer.class = "button:disabled";
        myLayer.disabled = "disabled";
   };
}

I have tried like above, but it is not working. I don't know where I am going wrong.