Count Descendants of an element

Question

I need some help write the logic for finding the number of descendants of an element.

html :

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <main>
        <ul>
          <li><button>item</button></li>
        </ul>
        <p>Hello, world</p>
      </main>
      <script src="index.js"></script>
</body>
</html>

index.js :

  function countDescendants(element) {}

  // Test code
  const result = countDescendants(document.querySelector("main"));
  if (result !== 4) {
    console.error(`fail: ${result}`);
  } else {
    console.log("Pass!");
  }

Can some help me to write the countDescendants function.We cant use built in function. should write our own logic. For this particular example it should return the result 4.

Mr Khan · Answer 1 · 2020-03-29T09:31:56.653

If you want all the children and descentants, the simplest way to do this is to use querySelectorAll this way:

document.querySelectorAll('main *').length

Complete code:

  // Test code
  const result = document.querySelectorAll("main *").length;
  if (result !== 4) {
    console.log(`fail: ${result}`);
  } else {
    console.log("Pass!");
  }

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <main>
        <ul>
          <li><button>item</button></li>
        </ul>
        <p>Hello, world</p>
      </main>
      <script src="index.js"></script>
</body>
</html>

How to get unique selector for an element: https://stackoverflow.com/a/66291608/4592648 Edit: you don't have to, just call querySelectorAll('*') on the node itself — Monday Fatigue, Nov 09 '21 at 12:39

score 0 · Answer 2 · answered Mar 30 '20 at 16:23

The following code uses the .children property of each element and recursively walks the DOM tree, counting children as it goes.

function countDescendants(el) {
  function countChildren({ children }) {
    let count = 0
    if(!children.length) return 0
    for(let el of [...children]) {
      count++
      count += countChildren(el)
    }
    return count
  }
  return countChildren(el)
}
const result = countDescendants(document.querySelector('main'))
console.log(result) // 4

<main>
  <ul>
    <li><button>item</button></li>
  </ul>
  <p>Hello, world</p>
</main>

Monday Fatigue · Answer 3 · 2021-11-11T06:54:20.860

0

Use Element.querySelectorAll()

The Element method querySelectorAll() returns a static (not live) NodeList representing a list of elements matching the specified group of selectors which are descendants of the element on which the method was called.

function countDescendants(el) {
  return el.querySelectorAll('*').length
}

edited Nov 11 '21 at 06:54

answered Nov 09 '21 at 12:41

Monday Fatigue

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Count Descendants of an element

3 Answers3