Native approach

document.getElementsByClassName('words')[0].getElementsByTagName('br').length

You could count the number of newlines in the text representation of your node (found via innerText property), or count the number of <br> tags with jQuery:

$('.words').each(function() {
  // count newlines
  const lines = (this.innerText.match(/n/g) || '').length
  console.log(lines);
  // or, count tags
  console.log($('br', this).length);
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="words-container">
  <div class="words">
    here are words<br>
    here are words<br>
    here are words<br>
    here are words<br>
  </div>
</div>

Note that I’m doing a .each() here, because $('.words') doesn’t strictly resolve to just one element, it’s a group of elements.

In order the find the number of tags, I use the initialiser variant with context to select the <br> tags inside of this (which is each element with words class.

If you just want to count direct descendent <br> elements inside all parents with word class, you’d do

$('.words > br').length

Please checkout this.

<div class="words-container">
  <div class="words">
    here are words<br>
    here are words<br>
    here are words<br>
    here are words<br>
  </div>
</div>
<script>
    $countWords = $('.words-container')
    if ($countWords.length) {
        var hahaha = $('.words').find('br').length
        alert(hahaha)
    }
</script>

Like this:

console.log($('.words-container .words br').length) // 4

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="words-container">
  <div class="words">
    here are words<br>
    here are words<br>
    here are words<br>
    here are words<br>
  </div>
</div>

Let’s say I have:

<div class="words-container">
  <div class="words">
    here are words<br>
    here are words<br>
    here are words<br>
    here are words<br>
  </div>
</div>

Using Javascript or jQuery, how would I count the exact amount of <br> tags that are populated in the “words” div? I need a way to know how many lines there are.

Not sure what I’m doing here:

$countWords = $('.words-container')
if ($countWords.length) {
  var hahaha = $('.words').find('<br>').length
  console.log(hahaha.length)
}