The numeric value of strings such as "1k" or "1m" is NaN.

Therefore, you may use Number.isNaN method to determine whether the string should be updated.
for example:

function increase (elem) {
    var previousValue = Number(elem.text());
    if (!Number.isNaN(previousValue)) {
        elem.text(previousValue + 1);
    }
}

increase($('.num_1'))

I have an updateable list

<ul>
  <li>
    <a class="one">posts <span class="num_1">1</span></a>
    <a class="two">followers <span class="num_2">999</span></a>
    <a class="three">following <span class="num_3">1K</span></a>
  </li>
</ul>

<button class="post-btn">Post</button>
<button class="follow-btn">Follow</button>

if a user updates the list by clicking either button and the number is below 1000, i want to get the text and add or subtract 1. if the number is above 1000, hence 1K, i want nothing to happen. all i have so far is this code which works for numbers under 1000 and not numbers abbbreviated as 1K

$('.num_1').text(Number($('.num_1').text())+1); or $('.num_1').text(Number($('.num_1').text())-1);

any help would be appreciated thanks