Contenteditable allowing only plain text [duplicate]

Answer 1

Use a textarea element instead of a contentEditable element: _{^{(emphasis mine)}}

The textarea element represents a multiline plain text edit control for the element's raw value.

Example:

/* Auto resize height */
var textarea = document.querySelector('textarea');
(textarea.oninput = function() {
  textarea.style.height = 0;
  textarea.style.height = textarea.scrollHeight + 'px';
})();

textarea { width: 100%; }

<textarea>Hello! You can edit my content. But only plain-text!!!</textarea>

Answer 2

Dirty hack to clean the pasted data.

function onpaste(e, el){
      setTimeout(function(){
            el.innerText = el.innerText;
        }, 10);
}