<script>
 
    var dhxWins = new dhtmlXWindows();
    ...
    // allow resizing
    dhxWins.window(id).allowResize();
    // deny resizing
    dhxWins.window(id).denyResize();
    // is resizable
    var isResizable = dhxWins.window(id).isResizable(); // true/false</script>