Most browsers will only allow copying of text from a visible input box or textarea

Copy function that multiple div boxes can use

  <style>
  .ClickToCopyBox
  {
    border: 1px solid #000;
    max-width: 600px;
    width: 100%;
    padding: 6px;
    box-sizing: border-box;
    overflow-wrap: break-word;
  }
  .ClickToCopyBox.Copied
  {
    background: #d4ffd4;
  }
  </style>

  <div class="ClickToCopyBox">
    Something that will be copied
  </div>

  <div class="ClickToCopyBox">
    Something else that will be copied
  </div>

  <div class="ClickToCopyBox" data-copy="Custom text to copy">
    This won't be copied, the data-copy="" text will be instead.
  </div>

  <script>
  function CopyElementText(element)
  {
    let text = element.innerText.trim();

    navigator.clipboard.writeText(text)
      .then(function()
      {
        element.classList.add('Copied');

        setTimeout(function()
        {
          element.classList.remove('Copied');
        }, 1000);
      })
      .catch(function(err)
      {
        console.error('Copy failed:', err);
      });
  }

  document.querySelectorAll('.ClickToCopyBox').forEach(function(el)
  {
    el.style.cursor = 'pointer';

    el.addEventListener('click', function()
    {
      CopyElementText(el);
    });
  });
  </script>

Providing different text to be copied than the text displayed

Add this to the div tab and it will be used instead:

data-copy="Custom text to copy"

Text area example for wordpress (jQuery)

This example overwrites the textarea value in case user has altered it

  <input id="MyElement1" type="textarea" onclick="this.select();  value="The text I want copied" >
  <a href="javascript:void(0);" onclick="CopyToClipboard('MyElement1', 'The text I want copied');" >Copy to clipboard</a>

    <script>   
      function CopyToClipboard(InputElementId, RequiredText) {
        document.getElementById(InputElementId).value = RequiredText;
        var copyText = document.getElementById(InputElementId);
        copyText.select();
        copyText.setSelectionRange(0, 99999); /* For mobile devices */
        document.execCommand("copy");
      
        alert("Copied to your clipboard");
      }
    </script>