getElementsByTagName does not return comment nodes in javascript
I want to retrieve all the nodes present in particular DIV element.see the below test page (firefox)
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<cite>谎友^ </cite>
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<span>2021-01-24 19:44</span>
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<pre><code>var getComments = function(oNode) {
var oChild,
aComments = [];
oNode = oNode || document;
for (var n=0; n<oNode.childNodes.length; n++) {
oChild = oNode.childNodes[n];
switch (oChild.nodeType) {
case 1: // Element
aComments = aComments.concat(getComments(oChild));
break;
case 8: // Comment
aComments.push(oChild);
break;
}
}
return aComments;
}
</code></pre>
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<span>2021-01-24 19:46</span>
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<p>Node types (non exhaustive):</p>
<ul>
<li>Element</li>
<li>Text</li>
<li>Comment</li>
</ul>
<p><code>getElementsByTagName</code> only picks up Element nodes. <code>childNodes</code>, <code>nextSibling</code>, etc. pick up all kinds of nodes. <code>nextElementSibling</code> only picks up Elements.</p>
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<p>Comments are nodes in the DOM tree, but they don't have a tag name. The <code>getElementsByTagName</code> method only returns nodes that have a tag name.</p>
<p>If you want all nodes, you have to traverse the DOM tree, using the <code>childNodes</code> collection of each element.</p>
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<input type="text" placeholder="不少于5个字" AUTOCOMPLETE="off" class="comment-input layui-input" name="content" />
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<span>2021-01-24 19:51</span>
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<p>The heart of the problem is that these methods...</p>
<pre><code>document.getElementById(...)
document.getElementsByTagName(...)
</code></pre>
<p>... return <em>elements</em>, as indicated by their names. However, comments and text nodes are not elements. They are nodes, but not elements.</p>
<p>So you need to do some traditional old fashioned DOM scripting, using <code>childNodes</code> like Vincent Robert suggested. Since - as you indicate in your comment to him - that <code>.childNodes</code> only goes one 'layer' deep, you need to define a recursive function to find the comment nodes: (I'm naming mine <code>document.getCommentNodes()</code>)</p>
<pre><code>document.getCommentNodes = function() {
function traverseDom(curr_element) { // this is the recursive function
var comments = new Array();
// base case: node is a comment node
if (curr_element.nodeName == "#comment" || curr_element.nodeType == 8) {
// You need this OR because some browsers won't support either nodType or nodeName... I think...
comments[comments.length] = curr_element;
}
// recursive case: node is not a comment node
else if(curr_element.childNodes.length>0) {
for (var i = 0; i<curr_element.childNodes.length; i++) {
// adventures with recursion!
comments = comments.concat(traverseDom(curr_element.childNodes[i]));
}
}
return comments;
}
return traverseDom(document.getElementsByTagName("html")[0]);
}
</code></pre>
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<span>2021-01-24 19:51</span>
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<p>You can use <code>.childNodes</code> to retrieve all children instead of <code>.getElementsByTagName('*')</code> which will only return child elements.</p>
<p>Here is a function to retrieve all descendants of a DOM node:</p>
<pre><code>function getDescendantNodes(node)
{
var ret = [];
if( node )
{
var childNodes = node.childNodes;
for( var i = 0, l = childNodes.length; i < l; ++i )
{
var childNode = childNodes[i];
ret.push(childNode);
ret = ret.concat(getDescendantNodes(childNode));
}
}
return ret;
}
</code></pre>
<p>Usage:</p>
<pre><code>getDescendantNodes(document.getElementById("foo"));
</code></pre>
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<p>If you don't care about IE, you could avoid the recursive approach and possibly improve performance (untested) by using a TreeWalker using document.createTreeWalker:</p>
<pre><code>function getCommentNodes(containerNode) {
var treeWalker = document.createTreeWalker(containerNode,
NodeFilter.SHOW_COMMENT, null, false);
var comments = [];
while (treeWalker.nextNode()) {
comments.push(treeWalker.currentNode);
}
return comments;
}
console.log(getCommentNodes(document.body));
</code></pre>
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