How to disable F12 in web

<script type=”text/javascript” language=”JavaScript”>// <![CDATA[
<br /><br />//////////F12 disable code////////////////////////<br /> document.onkeypress = function (event) {<br /> event = (event || window.event);<br /> if (event.keyCode == 123) {<br /> //alert(‘No F-12’);<br /> return false;<br /> }<br /> }<br /> document.onmousedown = function (event) {<br /> event = (event || window.event);<br /> if (event.keyCode == 123) {<br /> //alert(‘No F-keys’);<br /> return false;<br /> }<br /> }<br />document.onkeydown = function (event) {<br /> event = (event || window.event);<br /> if (event.keyCode == 123) {<br /> //alert(‘No F-keys’);<br /> return false;<br /> }<br /> }<br />/////////////////////end///////////////////////<br />
// ]]></script>