:nth-child(index/even/odd/equation)
匹配其父元素下的第N个子或奇偶元素
':eq(index)' 只匹配一个元素，而这个将为每一个父元素匹配子元素。:nth-child从1开始的，而:eq()是从0算起的！
可以使用:
nth-child(even)
:nth-child(odd)
:nth-child(3n)
:nth-child(2)
:nth-child(3n+1)
:nth-child(3n+2)
Matches the nth-child of its parent.
While ':eq(index)' matches only a single element, this matches more then one: One for each parent. The specified index is one-indexed, in contrast to :eq() which starst at zero.
返回值Array<Element>
参数index (Number) : 要匹配元素的序号，从1开始
示例在每个 ul 查找第 2 个li
HTML 代码:
<ul>
<li>John</li>
<li>Karl</li>
<li>Brandon</li>
</ul>
<ul>
<li>Glen</li>
<li>Tane</li>
<li>Ralph</li>
</ul>
jQuery 代码:
$("ul li:nth-child(2)")
结果:
[ <li>Karl</li>, <li>Tane</li> ]
--------------------------------------------------------------------------------
:first-child
匹配第一个子元素
':first' 只匹配一个元素，而此选择符将为每个父元素匹配一个子元素
Matches the first child of its parent.
While ':first' matches only a single element, this matches more then one: One for each parent.
返回值Array<Element>
示例在每个 ul 中查找第一个 li
HTML 代码:
<ul>
<li>John</li>
<li>Karl</li>
<li>Brandon</li>
</ul>
<ul>
<li>Glen</li>
<li>Tane</li>
<li>Ralph</li>
</ul>
jQuery 代码:
$("ul li:first-child")
结果:
[ <li>John</li>, <li>Glen</li> ]
--------------------------------------------------------------------------------
:last-child
匹配最后一个子元素
':last'只匹配一个元素，而此选择符将为每个父元素匹配一个子元素
Matches the last child of its parent.
While ':last' matches only a single element, this matches more then one: One for each parent.
返回值Array<Element>
示例在每个 ul 中查找最后一个 li
HTML 代码:
<ul>
<li>John</li>
<li>Karl</li>
<li>Brandon</li>
</ul>
<ul>
<li>Glen</li>
<li>Tane</li>
<li>Ralph</li>
</ul>
jQuery 代码:
$("ul li:last-child")
结果:
[ <li>Brandon</li>, <li>Ralph</li> ]
--------------------------------------------------------------------------------
:only-child
如果某个元素是父元素中唯一的子元素，那将会被匹配
如果父元素中含有其他元素，那将不会被匹配。
Matches the only child of its parent.
If the parent has other child elements, nothing is matched.
返回值Array<Element>
示例在 ul 中查找是唯一子元素的 li
HTML 代码:
<ul>
<li>John</li>
<li>Karl</li>
<li>Brandon</li>
</ul>
<ul>
<li>Glen</li>
jQuery 代码:
$("ul li:only-child")
结果:
[ <li>Glen</li> ]
--------------------------------------------------------------------------------
:input
匹配所有 input, textarea, select 和 button 元素
Matches all input, textarea, select and button elements.
返回值Array<Element>
示例查找所有的input元素
HTML 代码:
<form>
<input type="text" />
<input type="checkbox" />
<input type="radio" />
<input type="image" />
<input type="file" />
<input type="submit" />
<input type="reset" />
<input type="password" />
<input type="button" />
<select><option/></select>
<textarea></textarea>
<button></button>
</form>
jQuery 代码:
$(":input")
结果: