// javascript的单行注释符
两个斜杠是javascript的单行注释
oncontextmenu
Fires when the user clicks the right mouse button in the client area, opening the context menu，当用户右键单击页面的时候，打开一个右键菜单
return关键字,举例
<script language=”javascript”>
function myfunction(a,b){
var r;
r = a+b;
return(r)
}
window.alert(myfunction(3,2));
</script>