Issue #64  (isEqualNode() and Learning Tools)10/09/14

You can compare two nodes in an HTML document using the isEqualNode() method, supported in IE9+. The method is called on an existing node, and it's passed another node as the only argument.

Let's run some tests using the following HTML:
  <!-- test comment -->
  <!-- test comment -->
  <!-- test comment extra -->
  <!-- test comment extra-->
  <div class="one" id="two" data-extra="three">Testing</div>
  <div class="one" id="two" data-other="three">Testing</div>
  <div id="two" class="one" data-extra="three">Testing</div>
  <div class="one" id="two" data-extra="three">Testing </div>

Inside the body tag are some HTML comments and I've included three div elements with some text and various attributes on each. Notice the differences between the comment nodes as well as the differences between the element nodes. Now let's run some tests using isEqualNode():
var divs = document.getElementsByTagName('div'),
    myNodes = document.body.childNodes;

console.log(divs[0].isEqualNode(divs[1])); // false
console.log(divs[0].isEqualNode(divs[2])); // true
console.log(divs[1].isEqualNode(divs[2])); // false
console.log(divs[2].isEqualNode(divs[3])); // false
console.log(myNodes[1].isEqualNode(myNodes[3])); // true
console.log(myNodes[3].isEqualNode(myNodes[5])); // false
console.log(myNodes[5].isEqualNode(myNodes[7])); // false

(View on JS Bin) The first collection holds all the div elements, while the next collection holds all elements on the page, using the childNodes property. Let's look at the results of the tests on the div elements:
  • div elements 0 and 1 are not equal because one of the data-* attributes is different, even though the values are the same.
  • div elements 0 and 2 are equal, which is odd because they don't look equal. Note however, that for all practical purposes, they are equal. The only difference is the order of the attributes, which doesn't matter to isEqualNode().
  • div elements 1 and 2 are not equal for the same reason as 0 vs. 1.
  • div elements 2 and 3 are not equal, which is due to the single extra space in the text of the 3 element, before the closing tag.
Now what about the comment nodes?
  • These are collected using childNodes, which collects all nodes, including text nodes (white space), elements, and comments, so we have to reference the comments by skipping numbers in the indexes.
  • The first two comment nodes (1 and 3) are the same.
  • The 3 and 5 nodes are clearly different, having different text.
  • The last two nodes are also different but only because of the missing space at the tail end of the comment.
If you need an IE8 polyfill for this, you can try this DOM shim.

More info on MDN: Node.isEqualNode() and Node.childNodes.

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