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JQuery 位置选择器 详解

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:first       The first match of the page. (匹配找到的第一个元素)

声明         $("tr:first")

返回        

  <tr>
      <th>Language</th>
      <th>Type</th>
      <th>Invented</th>
  </tr>



:last       The last match of the page. (匹配找到的最后一个元素)

声明        $("tr:last")

返回        

<tr>
      <td>C++</td>
      <td>Static</td>
      <td>1983</td
</tr>


:first-child       The first child element. (匹配第一个子元素)

声明                 $("table tr:first-child")

                 或  $("tbody td:first-child")

返回

       $("table tr:first-child")

  <thead>
    <tr> …  </tr>
  </thead>
  <tbody>
    <tr>…   </tr>

     …

  </tbody>

$("tbody td:first-child")

<tbody>
    <tr> <td>Java</td
      …

    </tr>
    <tr> <td>Ruby</td
      …    </tr>
    <tr>
      <td>Smalltalk</td>
            …

    </tr>
    <tr>
      <td>C++</td
      ..

    </tr>
  </tbody>

image


:last-child        The last child element. (匹配最后一个子元素)

声明                  $("li:last-child")

返回                  和以上first-child相反,就不贴结果了。看图就可以了

image


:only-child         Returns all elements that have no siblings. (如果某个元素是父元素中唯一的子元素,那将会被匹配)

声明                   $("div label:only-child")

注意                   div中只有一个label,这才会被匹配,如果父元素中含有其他元素,那将不会被匹配。

image
对应HTML

<div><label>Some images:</label></div>


:nth-child(n)      The nth child element. (匹配其父元素下的第N个子或奇偶元素)

声明                     $("div image:nth-child(2)")

返回                     返回 绿色第二条

<div>
  <img src="images/image.1.jpg" id="hibiscus" alt="Hibiscus"/>
  <img src="images/image.2.jpg" id="littleBear" title="A dog named Little Bear"/>
  <img src="images/image.3.jpg" id="verbena" alt="Verbena"/>
  <img src="images/image.4.jpg" id="cozmo" title="A puppy named Cozmo"/>
  <img src="images/image.5.jpg" id="tigerLily" alt="Tiger Lily"/>
  <img src="images/image.6.jpg" id="coffeePot"/>
</div>

注意                     nth-child从1开始的,而:eq()是从0算起的!

其他形式

:nth-child(even)
:nth-child(odd)
:nth-child(3n)
:nth-child(2)
:nth-child(3n+1)
:nth-child(3n+2)


:nth-child(even|odd)    Even or odd children.  (返回偶数/奇数)

声明                               $("div image:nth-child(even)")

返回

<div>
  <img src="images/image.1.jpg" id="hibiscus" alt="Hibiscus"/>
  <img src="images/image.2.jpg" id="littleBear" title="A dog named Little Bear"/>
  <img src="images/image.3.jpg" id="verbena" alt="Verbena"/>
  <img src="images/image.4.jpg" id="cozmo" title="A puppy named Cozmo"/>
  <img src="images/image.5.jpg" id="tigerLily" alt="Tiger Lily"/>
  <img src="images/image.6.jpg" id="coffeePot"/>
</div>


:nth-child(Xn+Y)      The nth child element computed by the supplied formula. (倍数分组匹配)

声明       $("div:nth-child(3n+1)")

注意       这里比较难理解,仔细阅读

定义       先对元素进行分组,每组有a个,b为组内成员的序号,其中字母n和加号+不可缺省,位置不可调换,这是该写法的标志,

             其中a,b均为正整数或0。如3n+1、5n+1。但加号可以变为负号,此时匹配组内的第a-b个。

div:nth-child(3n+1)    匹配第1、第4、第7、…、每3个为一组的第1个div

div:nth-child(3n+5)    匹配第5、第8、第11、…、从第5个开始每3个为一组的第1个div

div:nth-child(5n-1)     匹配第5-1=4、第10-1=9、…、第5的倍数减1个div

div:nth-child(3n±0)    相当于(3n)

div:nth-child(±0n+3)  相当于(3)

图:

div:nth-child(3n+1)

image

对应的Html

<div>…</div>
<div>…</div> 第1个
<div id="someDiv">…</div>
<div title="myTitle2">…</div>
<div title="myTitle1">…</div> 第2个
  <div>…  </div>
  <div>…  </div> 第3个
  <div>…  </div>

div:nth-child(3n+2)

image

对应的Html

<div>…</div>第3个
<div>…</div>

<div id="someDiv">…</div>
<div title="myTitle1">…</div>第1个
<div title="myTitle2">…</div>


  <div>…  </div>第2个
  <div>…  </div>
  <div>…  </div>

:nth-child(-an+b)

此处一负一正,均不可缺省,否则无意义。这时与:nth-child(an+1)相似,都是匹配第1个,但不同的是它是倒着算的,从第b个开始往回算,所以它所匹配的最多也不会超过b个。

例子:

div:nth-child(-3n+8)   匹配第8、第5和第2个div

div:nth-child(-1n+8) 

      或(-n+8)              匹配前8个(包括第8个)div,这个较为实用点,用来限定前面N个匹配常会用到


:even and :odd      Even and odd matching elements page-wide. (匹配所有索引值为偶数的元素,从 0 开始计数)

声明       $("img:even")

返回     

<div>
  <img src="images/image.1.jpg" id="hibiscus" alt="Hibiscus"/>
  <img src="images/image.2.jpg" id="littleBear" title="A dog named Little Bear"/>
  <img src="images/image.3.jpg" id="verbena" alt="Verbena"/>
  <img src="images/image.4.jpg" id="cozmo" title="A puppy named Cozmo"/>
  <img src="images/image.5.jpg" id="tigerLily" alt="Tiger Lily"/>
  <img src="images/image.6.jpg" id="coffeePot"/>
</div>


:eq(n)        The nth matching element. (获取第N个元素)

声明            $("img:eq(2)")

返回     

<div>
  <img src="images/image.1.jpg" id="hibiscus" alt="Hibiscus"/>
  <img src="images/image.2.jpg" id="littleBear" title="A dog named Little Bear"/>
  <img src="images/image.3.jpg" id="verbena" alt="Verbena"/>
  <img src="images/image.4.jpg" id="cozmo" title="A puppy named Cozmo"/>
  <img src="images/image.5.jpg" id="tigerLily" alt="Tiger Lily"/>
  <img src="images/image.6.jpg" id="coffeePot"/>
</div>


:gt(n)         Matching elements after (and excluding) the nth matching element.(匹配所有大于给定索引值的元素)

声明             $("img:gt(2)")

返回     

<div>
  <img src="images/image.1.jpg" id="hibiscus" alt="Hibiscus"/>
  <img src="images/image.2.jpg" id="littleBear" title="A dog named Little Bear"/>
  <img src="images/image.3.jpg" id="verbena" alt="Verbena"/>
  <img src="images/image.4.jpg" id="cozmo" title="A puppy named Cozmo"/>
  <img src="images/image.5.jpg" id="tigerLily" alt="Tiger Lily"/>
  <img src="images/image.6.jpg" id="coffeePot"/>
</div>


:lt(n)           Matching elements before (and excluding) the nth matching element.(匹配所有小于给定索引值的元素

声明             $("img:lt(2)")

返回     

<div>
  <img src="images/image.1.jpg" id="hibiscus" alt="Hibiscus"/>
  <img src="images/image.2.jpg" id="littleBear" title="A dog named Little Bear"/>
  <img src="images/image.3.jpg" id="verbena" alt="Verbena"/>
  <img src="images/image.4.jpg" id="cozmo" title="A puppy named Cozmo"/>
  <img src="images/image.5.jpg" id="tigerLily" alt="Tiger Lily"/>
  <img src="images/image.6.jpg" id="coffeePot"/>
</div>


完整Html代码:

<table id="languages" border="0" cellspacing="1">
  <thead>
    <tr>
      <th>Language</th>
      <th>Type</th>
      <th>Invented</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>Java</td>
      <td>Static</td>
      <td>1995</td>
    </tr>
    <tr>
      <td>Ruby</td>
      <td>Dynamic</td>
      <td>1993</td>
    </tr>
    <tr>
      <td>Smalltalk</td>
      <td>Dynamic</td>
      <td>1972</td>
    </tr>
    <tr>
      <td>C++</td>
      <td>Static</td>
      <td>1983</td>
    </tr>
  </tbody>
</table>


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