Detailed explanation of jQuery traversal function

jQuery traversal functions include methods for filtering, finding, and concatenating elements.

函数 描述
.add() 将元素添加到匹配元素的集合中。
.andSelf() 把堆栈中之前的元素集添加到当前集合中。
.children() 获得匹配元素集合中每个元素的所有子元素。
.closest() 从元素本身开始，逐级向上级元素匹配，并返回最先匹配的祖先元素。
.contents() 获得匹配元素集合中每个元素的子元素，包括文本和注释节点。
.each() 对 jQuery 对象进行迭代，为每个匹配元素执行函数。
.end() 结束当前链中最近的一次筛选操作，并将匹配元素集合返回到前一次的状态。
.eq() 将匹配元素集合缩减为位于指定索引的新元素。
.filter() 将匹配元素集合缩减为匹配选择器或匹配函数返回值的新元素。
.find() 获得当前匹配元素集合中每个元素的后代，由选择器进行筛选。
.first() 将匹配元素集合缩减为集合中的第一个元素。
.has() 将匹配元素集合缩减为包含特定元素的后代的集合。
.is() 根据选择器检查当前匹配元素集合，如果存在至少一个匹配元素，则返回 true。
.last() 将匹配元素集合缩减为集合中的最后一个元素。
.map() 把当前匹配集合中的每个元素传递给函数，产生包含返回值的新 jQuery 对象。
.next() 获得匹配元素集合中每个元素紧邻的同辈元素。
.nextAll() 获得匹配元素集合中每个元素之后的所有同辈元素，由选择器进行筛选（可选）。
.nextUntil() 获得每个元素之后所有的同辈元素，直到遇到匹配选择器的元素为止。
.not() 从匹配元素集合中删除元素。
.offsetParent() 获得用于定位的第一个父元素。
.parent() 获得当前匹配元素集合中每个元素的父元素，由选择器筛选（可选）。
.parents() 获得当前匹配元素集合中每个元素的祖先元素，由选择器筛选（可选）。
.parentsUntil() 获得当前匹配元素集合中每个元素的祖先元素，直到遇到匹配选择器的元素为止。
.prev() 获得匹配元素集合中每个元素紧邻的前一个同辈元素，由选择器筛选（可选）。
.prevAll() 获得匹配元素集合中每个元素之前的所有同辈元素，由选择器进行筛选（可选）。
.prevUntil() 获得每个元素之前所有的同辈元素，直到遇到匹配选择器的元素为止。
.siblings() 获得匹配元素集合中所有元素的同辈元素，由选择器筛选（可选）。
.slice() 将匹配元素集合缩减为指定范围的子集。

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Usage of each

1.each in the array

 var arr = [ "one", "two", "three", "four"];   
 $.each(arr, function(){   
  alert(this);   
 });  
//上面这个each输出的结果分别为：one,two,three,four  
  
var arr1 = [[1, 4, 3], [4, 6, 6], [7, 20, 9]]   
$.each(arr1, function(i, item){   
  alert(item[0]);   
});   
//其实arr1为一个二维数组，item相当于取每一个一维数组，  
//item[0]相对于取每一个一维数组里的第一个值  
//所以上面这个each输出分别为：1  4  7   
 
 
var obj = { one:1, two:2, three:3, four:4};   
$.each(obj, function(i) {   
  alert(obj[i]);      
});  
//这个each就有更厉害了，能循环每一个属性   
//输出结果为：1  2 3 4

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2. Traverse Dom elements

<html>
<head>
<script type="text/javascript" src="/jquery/jquery.js"></script>
<script type="text/javascript">
$(document).ready(function(){
 $("button").click(function(){
  $("li").each(function(){
   alert($(this).text())
  });
 });
});
</script>
</head>
<body>
<button>输出每个列表项的值</button>
<ul>
<li>Coffee</li>
<li>Milk</li>
<li>Soda</li>
</ul>
</body>
</html>

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Coffee, Milk, and Soda pop up in sequence

3. Comparison between each and map

The following example is to obtain the ID value of each multi-box;

each method:

Define an empty array and add ID values to the array through the each method; finally, after converting the array into a string, alert the value;

$(function(){
  var arr = [];
  $(":checkbox").each(function(index){
    arr.push(this.id);
  });
  var str = arr.join(",");
  alert(str);
})

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map method:

Execute return this.id for each :checkbox; and automatically save these return values as jQuery objects, then use the get method to convert them into native Javascript arrays, then use the join method to convert them into strings, and finally alert This value;

$(function(){
  var str = $(":checkbox").map(function() {
    return this.id;
  }).get().join();  
  alert(str);
})

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When you need the value of an array, use the map method, which is very convenient.

4. Use each

in jquery

Loop through an array, using both element index and content. (i is the index, n is the content)

The code is as follows:

$.each( [0,1,2], function(i, n){
alert( "Item #" + i + ": " + n );
});

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Iterate over the object, using both member names and variable contents. (i is the member name, n is the variable content)
The code is as follows:

$.each( { name: "John", lang: "JS" }, function(i, n){
alert( "Name: " + i + ", Value: " + n );
});

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Example the DOM elements, taking an input form element as an example.
If you have a piece of code like this in your dom

<input name="aaa" type="hidden" value="111" /> 
<input name="bbb" type="hidden" value="222" /> 
<input name="ccc" type="hidden" value="333" /> 
<input name="ddd" type="hidden" value="444"/>

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Then you use each as follows

The code is as follows:

$.each($("input:hidden"), function(i,val){
alert(val); //输出[object HTMLInputElement]，因为它是一个表单元素。
alert(i); //输出索引为0，1，2，3
alert(val.name); //输出name的值
alert(val.value); //输出value的值
});

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Find elements based on this in 5.each

To achieve the effect, the word "Reply" will only be displayed when the mouse passes over it

<ol class="commentlist">
  <li class="comment">
    <div class="comment-body">
     <p>嗨，第一层评论</p>
     <div class="reply">
      <a href="#" class=".comment-reply-link">回复</a>
     </div>
    </div>
    <ul class="children">
     <li class="comment">
      <div class="comment-body">
      <p>第二层评论</p>
      <div class="reply">
       <a href="#" class=".comment-reply-link">回复</a>
      </div>
     </div></li>
    </ul>
  </li>
</ol>

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The js code is as follows

$("div.reply").hover(function(){
 $(this).find(".comment-reply-link").show();
},function(){
 $(this).find(".comment-reply-link").hide();
});

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Achieve the effect and verify whether all judgment questions have options

html

<ul id="ulSingle">
  
      <li class="liStyle">
        1. 阿斯顿按时<label id="selectTips" style="display: none" class="fillTims">请选择</label>
        <!--begin选项-->
        <ul>
          
              <li class="liStyle2">
                <span id="repSingle_repSingleChoices_0_labOption_0">A     </span>.阿萨德发<input type="hidden" name="repSingle$ctl00$repSingleChoices$ctl00$hidID" id="repSingle_repSingleChoices_0_hidID_0" value="1" />
                <input id="repSingle_repSingleChoices_0_cheSingleChoice_0" type="checkbox" name="repSingle$ctl00$repSingleChoices$ctl00$cheSingleChoice" /></li>
            
              <li class="liStyle2">
                <span id="repSingle_repSingleChoices_0_labOption_1">B     </span>.阿萨德发<input type="hidden" name="repSingle$ctl00$repSingleChoices$ctl01$hidID" id="repSingle_repSingleChoices_0_hidID_1" value="2" />
                <input id="repSingle_repSingleChoices_0_cheSingleChoice_1" type="checkbox" name="repSingle$ctl00$repSingleChoices$ctl01$cheSingleChoice" /></li>
            
              <li class="liStyle2">
                <span id="repSingle_repSingleChoices_0_labOption_2">C     </span>.阿斯顿<input type="hidden" name="repSingle$ctl00$repSingleChoices$ctl02$hidID" id="repSingle_repSingleChoices_0_hidID_2" value="3" />
                <input id="repSingle_repSingleChoices_0_cheSingleChoice_2" type="checkbox" name="repSingle$ctl00$repSingleChoices$ctl02$cheSingleChoice" /></li>
            
        </ul>
        <!--end选项-->
        <br />
      </li>
    
</ul>

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js code

//验证单选题是否选中
    $("ul#ulSingle>li.liStyle").each(function (index) {
      //选项个数
      var count = $(this).find("ul>li>:checkbox").length;
      var selectedCount = 0
      for (var i = 0; i < count; i++) {
        if ($(this).find("ul>li>:checkbox:eq(" + i + ")").attr("checked")) {
          selectedCount++;
          break;
        }
      }
      if (selectedCount == 0) {
        $(this).find("label#selectTips").show();
        return false;
      }
      else {
        $(this).find("label#selectTips").hide();
      }
    })

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6.Official explanation

The following is the official explanation:

jQuery.each(object, [callback])

Overview
A general iteration method that can be used to iterate objects and arrays.

Unlike the $().each() method that iterates over jQuery objects, this method can be used to iterate over any object. The callback function has two parameters: the first is the member of the object or the index of the array, and the second is the corresponding variable or content. If you need to exit the each loop, you can make the callback function return false, and other return values will be ignored.

Parameters
objectObject
The object or array to be traversed.

callback (optional)Function
Callback function executed for each member/element.

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