CSS中的高级计数器

CSS中的计数器

总所周知CSS中是可以使用计数器的：

<!-- html -->
<ol class="list">  
    <li>a</li>
    <li>b</li>
    <li>c</li>
</ol>  
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<!-- css -->
.list {
    counter-reset: i; //reset conunter
}
.list > li {
    counter-increment: i; //counter ID
}
.list li:after {
    content: "[" counter(i) "]"; //print the result
}
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我们定义了一个ID在counter-reset属性中作为初始值（默认为0）。你可以设置另一个值在counter-increment属性中作为每一步的递增值。

高级CSS计数器

你可以计算出有多少个复选框被用户勾选了：

<!-- html -->
<div class="languages">  
  <input id="c" type="checkbox"><label for="c">C</label>
  <input id="C++" type="checkbox"><label for="C++">C++</label>
  <input id="C#" type="checkbox"><label for="C#">C#</label>
  <input id="Java" type="checkbox"><label for="Java">Java</label>
  <input id="JavaScript" type="checkbox"><label for="JavaScript">JavaScript</label>
  <input id="PHP" type="checkbox"><label for="PHP">PHP</label>
  <input id="Python" type="checkbox"><label for="Python">Python</label>
  <input id="Ruby" type="checkbox"><label for="Ruby">Ruby</label>
</div>  
<p class="total">  
  Total selected:
</p>  
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<!-- css -->
.languages {
  counter-reset: characters;
}
input:checked {  
  counter-increment: characters;
}
.total:after {
  content: counter(characters);
} 
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你也可以制作一个简单的计算器：

<!-- html -->
<div class="numbers">  
  <input id="one" type="checkbox"><label for="one">1</label>
  <input id="two" type="checkbox"><label for="two">2</label>
  <input id="three" type="checkbox"><label for="three">3</label>
  <input id="four" type="checkbox"><label for="four">4</label>
  <input id="five" type="checkbox"><label for="five">5</label>
  <input id="one-hundred" type="checkbox"><label for="one-hundred">100</label>
</div>  
<p class="sum">  
  Sum 
</p>  
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<!-- css -->
.numbers {
  counter-reset: sum;
}

#one:checked { counter-increment: sum 1; }
#two:checked { counter-increment: sum 2; }
#three:checked { counter-increment: sum 3; }
#four:checked { counter-increment: sum 4; }
#five:checked { counter-increment: sum 5; }
#one-hundred:checked { counter-increment: sum 100; }

.sum::after {
  content: '= ' counter(sum);
} 
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它同样得以运行，请看具体的DEMO和文章。