Tabs

<div class="tabs_wrap">
  <div class="tabs_container">
    <button class="btn tab tab--1 tab--active" data-tab="1">
      tab button 1
    </button>
    <button class="btn tab tab--2 tab--active"  data-tab="2">
      tab button 2
    </button>
  </div>
  <div class="content content--1 content--active">
    <div>
      contents 1
    </div>
  </div>
  <div class="content content--2 content--active">
    <div>
      contents 2
    </div>
  </div>
</div>  

const tabs = document.querySelectorAll('.tab');
const tabsContainer = document.querySelector('.tabs_container');
const tabsContent = document.querySelectorAll('.content');

tabsContainer.addEventListener('click', function (e) {
  const clicked = e.target.closest('.tab');

  // Guard clause
  if (!clicked) return;

  // Remove active classes
  tabs.forEach(t => t.classList.remove('tab--active'));
  tabsContent.forEach(c => c.classList.remove('content--active'));

  // Activate tab
  clicked.classList.add('tab--active');

  // Activate content area

 document.querySelector(`.content-${clicked.dataset.tab}`).classList.add('content--active');
});

Avoid using forEach to attach events to each tab. Instead, leverage event bubbling to set an event listener on the parent element and determine which child element it corresponds to.