Javascript F12 Engelleme

<script>
    // Sağ tıklama engelle
    document.addEventListener('contextmenu', event => event.preventDefault());
 
    document.onkeydown = function (e) {
 
        // F12 Engelle
        if(e.keyCode == 123) {
            return false;
        }
 
        // CTRL+I Engelle
        if(e.ctrlKey && e.shiftKey && e.keyCode == 73){
            return false;
        }
 
        // CTRL+J Engelle
        if(e.ctrlKey && e.shiftKey && e.keyCode == 74) {
            return false;
        }
 
        // CTRL+U Engelle
        if(e.ctrlKey && e.keyCode == 85) {
            return false;
        }
    }
 
</script>