1.question:

when first operate the checkbox with sentence like :

$("input[type=checkbox]").attr("checked",true);

$("input[type=checkbox]").attr("checkec",false);

it will succeed;

but the second time , it will failed.why??

2.Cause:

if the attribute name of the tag is belong to the tag(the html defined), the prop(name,value) method works,

if the attribute name of the tag is custom , then attr(name, value) method works.

3. Solution:

$("input[type=checkbox]").prop("checked",true);

$("input[type=checkbox]").prop("checked",false);

it works.