<script type="text/javascript">
    window.onload = function(event) {
        // your code here
    };

    // equivalent with jQuery (when window loads)

    jQuery(window).load(function(event) {
        // your code here
    });

    // alternatively with jQuery (when DOM is ready)

    jQuery(document).ready(function(event) {
        // your code here
    });

    // you can also call a function if this <script>-block is reached (loaded) first time
    // place the <script>-block before body-tag is closing and you have nearly what DOM-ready does.
    someFunction();
</script>