js禁止右击，禁止浏览器菜单

function click() {
return false; }
function click1() {
if (event.button==2) { return false; }}
function CtrlKeyDown(){
if (event.ctrlKey) { return false; }}
document.onkeydown=CtrlKeyDown;
document.onselectstart=click;
document.onmousedown=click1;
document.oncontextmenu=function(event) {
    if (document.all) 
        window.event.returnValue = false;// for IE
    else 
        event.preventDefault();
}