CODEWITHSUNDEEP
javascriptdomselectors-api
chavab_1
chavab_1

Reputation: 237

queryselectorAll with descendant not selecting correctly

I have the following DOM structure:

    var parent = document.querySelector(".test");
    var navChild = parent.querySelectorAll("ul > li > a");
    for (i = 0; i < navChild.length; i++) {
            navChild[i].style.backgroundColor = "red";
        }
    console.log(navChild.lenght);
    console.log(navChild);
<!-- begin snippet: js hide: false console: true babel: false -->
    <ul>
      <li class="test">
        <a>ssss</a> <!--this will also be affected -->
        <ul>
          <li><a>fsfsf</a></li>
          <li><a>sff</a></li>
          <li><a>ggg</a></li>
        </ul>
      </li>
    </ul>

I want to select the 3 a tags using vanilla javascript and starting from the li with the class test. I put this in a parent variable and then use querySelectorAll to try to get only the a tags that are inside the next list. However, the nodelist that is returned also includes the very first a tag even though it's not a descendant. This is my code:

var navChild = parent.querySelectorAll("ul > li > a");

What's really weird is that if I query for just the li descendants I get only the 3. So I don't understand why when I query for the child descendant of that li I also get that first a tag that is two levels up on the DOM.

I know I could do this using jQuery but I don't want to use it.

EDITED to show how I'm setting the parent variable

I'm trying to add those a tags to the childs variable after I've hit the enter keyboard button while on the first a tag that I don't want to include in the childs node list.

var alinks = document.querySelectorAll('.test > a');
[].forEach.call(alinks, function(link){
    link.addEventListener('keyup', function(e){
        e.preventDefault();
        if(e.keyCode === 13) {
            var linkParent = e.target.parentElement;
            var childs = menuParent.querySelectorAll('ul > li > a');
        }        
    })
});

When I log linkParent it is correctly being set as the li with class test. I don't understand why then if I run the query from there it still includes the very first a tag. As I previously stated, if I query just ul > li it gives me the correct li tags.

Upvotes: 3

Views: 2798

Answers (3)

skyline3000
skyline3000

Reputation: 7913

This is because the first <a> tag you're trying to ignore still falls into the selector rule ul > li > a. So, even though you start the query with the <li class="test"> as the root (which does work by the way, I don't know why the other answers say that the document is still the root), the first child element it finds is the <a> tag and, indeed, it is the child of an <li> which is the child of a <ul>. The fact that this winds up going "above" your specified root is ignored.

Edit: If you want the selector rule to be scoped to the root as well, you can use this instead:

parent.querySelectorAll(":scope ul > li > a");

And to further clarify, browser CSS engines evaluate CSS rules right-to-left. In your mind, you want the browser to start at the root (the parent <li class="test">) and then find a <ul> tag and then find a <li> tag and then find an <a> tag.

However, the browser starts with the root, but then looks for all of the <a> tags below the root. Then it checks if the <a> tag is within an <li> and then if the <li> is within a <ul>. So the <li class="parent"> tag really is the root, but it does not follow the left-to-right hierarchy of your selector rule after that, it goes right-to-left.

Upvotes: 3

CertainPerformance
CertainPerformance

Reputation: 370729

It's because your first <a> also matches ul > li > a, and since said a is still a descendant of the element qSA was called upon, it gets included in the NodeList.

https://developer.mozilla.org/en-US/docs/Web/API/Element/querySelectorAll#Javascript

Element.querySelector and Element.querySelectorAll are somewhat quirky in that respect: although the only matching elements must be children of the Element you called it on, the selector string still starts at the document level - it doesn't verify the selector by isolating the element and its descendants first.

const child = document.querySelector('#child');
const span = child.querySelector('#parent span');
console.log(span.textContent);
<div id="parent">
<div id="child">
<span>text</span>
</div>
</div>

Upvotes: 1

mcv
mcv

Reputation: 1460

Use this to define your var navChild = document.querySelectorAll("test > ul > li > a");. I had to use a running example to solve the issue. This will get the 3 vanilla <a> you want

The querySelectorAll() method returns all elements in the document that matches a specified CSS selector(s), as a static NodeList object.

I presume this is true even when you set a parent within the document.

var navChild = document.querySelectorAll(".test > ul > li > a");
for (i = 0; i < navChild.length; i++) {
        navChild[i].style.backgroundColor = "red";
}
//console.log(navChild.lenght);
//console.log(navChild);
<ul>
  <li class="test">
    <a>qqqq</a>
    <ul>
      <li><a>aaa</a></li>
      <li><a>bbb</a></li>
      <li><a>ccc</a></li>
    </ul>
  </li>
</ul>

Upvotes: 0

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