How to run JavaScript code before page load?

I have working in asp.net web application. Here I need to run JavaScript before page load.

I have tried:

<body oninit="funinit();" onprerender="funRender();" onload="funload();">


</body>

 <script type="text/javascript" language="javascript">
    function funinit() {
        alert("funinit");
    }
    function funload() {
        alert("funload");
    }
    function funRender() {
        alert("funRender");
    }      

</script>

here only funload() is working.