使用Style.display 样式时，
显示对象用 obj.style.display = "block";
隐藏对象用 obj.style.display = "none"
附：display 语法
Syntax
HTML { display : sDisplay } Scripting object.style.display [ = sDisplay ]
Possible Values
sDisplay String that specifies or receives one of the following values.
block Object is rendered as a block element. none Object is not rendered. inline Default. Object is rendered as an inline element sized by the dimensions of the content. inline-block Object is rendered inline, but the contents of the object are rendered as a block element. Adjacent inline elements are rendered on the same line, space permitting. list-item 
Internet Explorer 6 and later. Object is rendered as a block element, and a list-item marker is added. table-header-group Table header is always displayed before all other rows and row groups, and after any top captions. The header is displayed on each page spanned by a table. table-footer-group Table footer is always displayed after all other rows and row groups, and before any bottom captions. The footer is displayed on each page spanned by a table.