问题
I want to find a <td role="foo" class="one two three four"> within a <div id="myid">
These two selectors work:
$('#myid td[role=foo]')
$('#myid .two')
But this one doesn't, why?
$('#myid .two td[role=foo]')
回答1:
Because a space in a selector string is a descendant-selector.
You would need to do:
$('#myid td.two[role=foo]')
The way you had it, you were searching for <td role="foo"> elements that are a descendant of .two.
回答2:
Because your selector:
$('#myid .two td[role=foo]')
is looking for a td[role=foo] within an element of class .two within an element of id #myid.
You're using descendant selectors, rather than looking for td[role=foo].two which, I think, is what you want.
回答3:
You want:
$("#myid td[role=foo].two")...
This selector:
$('#myid .two td[role=foo]')
means: find the element with ID "myid". From it find all descendants with a class of "two". From those elements find all descendants <td> elements that have a role attribute with a value of "foo".
来源：https://stackoverflow.com/questions/3814966/help-understanding-jquery-attribute-equals-selector