<div class="selected_body"  id='d1'>
  <article class="item">
     куча кода
  </article>
  <article class="item">
    куча кода
  </article>
  <article class="item">
    куча кода
  </article>
</div>

<div class="selected_body" id='d2'>
  <article class="item">
     куча кода
  </article>
  <article class="item">
    куча кода
  </article>
  <article class="item">
    куча кода
  </article>
</div>
<div id="result"></div>

document.addEventListener('DOMContentLoaded', function(e) {
  const resEl = document.querySelector('#result')
  let array = document.querySelectorAll('div.selected_body')
    array.forEach((item) => {
        console.log(item.offsetHeight)
        resEl.innerHtml += `${item.getAttribute('id')} : ${item.offsetHeight}  <br>`
    })
  
})