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Detailed explanation of usage examples of jQuery is() function

零下一度Original: 2017-06-19 14:22:361378browse

The is() method in jquery can determine whether an element is visible, hidden, or selected.

Below we introduce examples respectively.

1. Determine whether the element is hidden
The p element in the following html is hidden:

<!doctype html>
<html>
<head>
<script src="jquery-1.7.2.min.js"></script>
</head>
<body>
    <p id="test" style="display:none">你看不到我</p>
<span ></span>
    <script type="text/
javascript
">
$(&#39;span&#39;).html(&#39;test p is visible? &#39; + $(&#39;#test&#39;).is(&#39;:visible&#39;));
    </script>
</body>
</html>

2. Determine whether the checkbox is selected
You can pass xx in jquery. is(':checked') determines whether checkbox and radiobutton are selected, as follows to test html

<!doctype html>
<html>
<head>
<script src="jquery-1.7.2.min.js"></script>
</head>
<body>
<p>
    <input type="checkbox" name="chkChecked" checked="checked"/> chkChecked
    <input type="checkbox" name="chkNoChecked" /> chkNoChecked
</p>
<span ></span>
    <script type="text/javascript">
$(&#39;span&#39;).html(&#39;chkChecked checked? &#39; + $(&#39;input[name=chkChecked]&#39;).is(&#39;:checked&#39;) + &#39;<br/> &#39;
    +&#39;chkNoChecked checked? &#39; + $(&#39;input[name=chkNoChecked]&#39;).is(&#39;:checked&#39;) );
    </script>
</body>
</html>

3. Determine whether a certain style is used

<html lang="en">
<head>
  <meta charset="utf-8">
  <title>is函数介绍</title>
  <style>  //设置一些基本样式
  p { width:60px; height:60px; margin:5px; float:left;
      border:4px outset; 
background
:green; text-align:center;
      
font-weight
:bolder; cursor:pointer; }
  .blue { background:blue; }  //样式1
  .red { background:red; }//样式2
  span { color:white; font-size:16px; }
  p { color:red; font-weight:bolder; background:yellow;
      margin:3px; clear:left; display:none; }
  </style>
  <script src="jquery-1.9.1.js"></script> //注意 这里使用的是jQuery官方的脚步库
</head>
<body>
  <p></p>  //注意这里出现了第一个p
<p class="blue"></p>//注意这里出现了第2个p
<p></p>//注意这里出现了第3个p
<p class="red"></p>//注意这里出现了第4个p
<p><br/><span>Peter</span></p>//注意这里出现了第5个p
<p class="blue"></p>//注意这里出现了第6个p
<p> 脚本学堂，www.jbxue.com。</p>
<script> 
  $("p").one(&#39;click&#39;, function () {   //$("p").one  代表对p元素附加一个事件，
//还能附加多个事件 譬如click或者mouseout时同时执行一些事情
    if ($(this).is("
:first-child
")) { //is函数发挥作用了，is(":first-child") 代表 
   //判断此p是否第一个出现的p
      $("p").text("It&#39;s the first p."); //text和html区别在于是否支持html标记
  // 此时你在里面写个 alert是不会执行的
    } else if ($(this).is(".blue,.red")) {  //判断该p是否 具有blue或者red的 class
      $("p").text("这是个蓝色或者红色的p");
    } else if ($(this).is(":contains(&#39;Peter&#39;)")) { //判断p中是否存在Peter这个词
      $("p").text("It&#39;s Peter!");
    } else {
      $("p").html("It&#39;s nothing <em>special</em>.");
    }
    $("p").hide().slideDown("slow"); //这是一个动画效果。慢慢展现p的内容
    $(this).css({"
border-style
": "inset", cursor:"default"});
  });
</script>
</body>
</html>

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