jquery gets all selected checkboxes with a specific name, supports IE9 standard mode_jquery

The original statement is var selectChks = $("input[type=checkbox][name=productItem][checked]");
It can be obtained normally in IE7, IE8 and IE9 compatibility modes
But in It cannot be obtained in IE9 standard mode. The length is always 0
So I checked the information and found the following writing method
var selectChks = $("input[type=checkbox][name=productItem]:checked");
After testing, it can also be used normally in IE7, IE8 and IE9 compatibility modes, and IE9 standard mode