JavaScript get clipboard data on paste event (Cross browser)

Question

How can a web application detect a paste event and retrieve the data to be pasted?

I would like to remove HTML content before the text is pasted into a rich text edi

Answer 1

This should work on all browsers that support the onpaste event and the mutation observer.

This solution goes a step beyond getting the text only, it actually allows you to edit the pasted content before it get pasted into an element.

It works by using contenteditable, onpaste event (supported by all major browsers) en mutation observers (supported by Chrome, Firefox and IE11+)

step 1

Create a HTML-element with contenteditable

step 2

In your Javascript code add the following event

document.getElementById("target_paste_element").addEventListener("paste", pasteEventVerifierEditor.bind(window, pasteCallBack), false);

We need to bind pasteCallBack, since the mutation observer will be called asynchronously.

step 3

Add the following function to your code

function pasteEventVerifierEditor(callback, e)
{
   //is fired on a paste event. 
    //pastes content into another contenteditable div, mutation observer observes this, content get pasted, dom tree is copied and can be referenced through call back.
    //create temp div
    //save the caret position.
    savedCaret = saveSelection(document.getElementById("target_paste_element"));

    var tempDiv = document.createElement("div");
    tempDiv.id = "id_tempDiv_paste_editor";
    //tempDiv.style.display = "none";
    document.body.appendChild(tempDiv);
    tempDiv.contentEditable = "true";

    tempDiv.focus();

    //we have to wait for the change to occur.
    //attach a mutation observer
    if (window['MutationObserver'])
    {
        //this is new functionality
        //observer is present in firefox/chrome and IE11
        // select the target node
        // create an observer instance
        tempDiv.observer = new MutationObserver(pasteMutationObserver.bind(window, callback));
        // configuration of the observer:
        var config = { attributes: false, childList: true, characterData: true, subtree: true };

        // pass in the target node, as well as the observer options
        tempDiv.observer.observe(tempDiv, config);

    }   

}



function pasteMutationObserver(callback)
{

    document.getElementById("id_tempDiv_paste_editor").observer.disconnect();
    delete document.getElementById("id_tempDiv_paste_editor").observer;

    if (callback)
    {
        //return the copied dom tree to the supplied callback.
        //copy to avoid closures.
        callback.apply(document.getElementById("id_tempDiv_paste_editor").cloneNode(true));
    }
    document.body.removeChild(document.getElementById("id_tempDiv_paste_editor"));

}

function pasteCallBack()
{
    //paste the content into the element.
    restoreSelection(document.getElementById("target_paste_element"), savedCaret);
    delete savedCaret;

    pasteHtmlAtCaret(this.innerHTML, false, true);
}   


saveSelection = function(containerEl) {
if (containerEl == document.activeElement)
{
    var range = window.getSelection().getRangeAt(0);
    var preSelectionRange = range.cloneRange();
    preSelectionRange.selectNodeContents(containerEl);
    preSelectionRange.setEnd(range.startContainer, range.startOffset);
    var start = preSelectionRange.toString().length;

    return {
        start: start,
        end: start + range.toString().length
    };
}
};

restoreSelection = function(containerEl, savedSel) {
    containerEl.focus();
    var charIndex = 0, range = document.createRange();
    range.setStart(containerEl, 0);
    range.collapse(true);
    var nodeStack = [containerEl], node, foundStart = false, stop = false;

    while (!stop && (node = nodeStack.pop())) {
        if (node.nodeType == 3) {
            var nextCharIndex = charIndex + node.length;
            if (!foundStart && savedSel.start >= charIndex && savedSel.start <= nextCharIndex) {
                range.setStart(node, savedSel.start - charIndex);
                foundStart = true;
            }
            if (foundStart && savedSel.end >= charIndex && savedSel.end <= nextCharIndex) {
                range.setEnd(node, savedSel.end - charIndex);
                stop = true;
            }
            charIndex = nextCharIndex;
        } else {
            var i = node.childNodes.length;
            while (i--) {
                nodeStack.push(node.childNodes[i]);
            }
        }
    }

    var sel = window.getSelection();
    sel.removeAllRanges();
    sel.addRange(range);
}

function pasteHtmlAtCaret(html, returnInNode, selectPastedContent) {
//function written by Tim Down

var sel, range;
if (window.getSelection) {
    // IE9 and non-IE
    sel = window.getSelection();
    if (sel.getRangeAt && sel.rangeCount) {
        range = sel.getRangeAt(0);
        range.deleteContents();

        // Range.createContextualFragment() would be useful here but is
        // only relatively recently standardized and is not supported in
        // some browsers (IE9, for one)
        var el = document.createElement("div");
        el.innerHTML = html;
        var frag = document.createDocumentFragment(), node, lastNode;
        while ( (node = el.firstChild) ) {
            lastNode = frag.appendChild(node);
        }
        var firstNode = frag.firstChild;
        range.insertNode(frag);

        // Preserve the selection
        if (lastNode) {
            range = range.cloneRange();
            if (returnInNode)
            {
                range.setStart(lastNode, 0); //this part is edited, set caret inside pasted node.
            }
            else
            {
                range.setStartAfter(lastNode); 
            }
            if (selectPastedContent) {
                range.setStartBefore(firstNode);
            } else {
                range.collapse(true);
            }
            sel.removeAllRanges();
            sel.addRange(range);
        }
    }
} else if ( (sel = document.selection) && sel.type != "Control") {
    // IE < 9
    var originalRange = sel.createRange();
    originalRange.collapse(true);
    sel.createRange().pasteHTML(html);
    if (selectPastedContent) {
        range = sel.createRange();
        range.setEndPoint("StartToStart", originalRange);
        range.select();
    }
}
}

What the code does:

1. Somebody fires the paste event by using ctrl-v, contextmenu or other means
2. In the paste event a new element with contenteditable is created (an element with contenteditable has elevated privileges)
3. The caret position of the target element is saved.
4. The focus is set to the new element
5. The content gets pasted into the new element and is rendered in the DOM.
6. The mutation observer catches this (it registers all changes to the dom tree and content). Then fires the mutation event.
7. The dom of the pasted content gets cloned into a variable and returned to the callback. The temporary element is destroyed.
8. The callback receives the cloned DOM. The caret is restored. You can edit this before you append it to your target. element. In this example I'm using Tim Downs functions for saving/restoring the caret and pasting HTML into the element.

Example

document.getElementById("target_paste_element").addEventListener("paste", pasteEventVerifierEditor.bind(window, pasteCallBack), false);


function pasteEventVerifierEditor(callback, e) {
  //is fired on a paste event. 
  //pastes content into another contenteditable div, mutation observer observes this, content get pasted, dom tree is copied and can be referenced through call back.
  //create temp div
  //save the caret position.
  savedCaret = saveSelection(document.getElementById("target_paste_element"));

  var tempDiv = document.createElement("div");
  tempDiv.id = "id_tempDiv_paste_editor";
  //tempDiv.style.display = "none";
  document.body.appendChild(tempDiv);
  tempDiv.contentEditable = "true";

  tempDiv.focus();

  //we have to wait for the change to occur.
  //attach a mutation observer
  if (window['MutationObserver']) {
    //this is new functionality
    //observer is present in firefox/chrome and IE11
    // select the target node
    // create an observer instance
    tempDiv.observer = new MutationObserver(pasteMutationObserver.bind(window, callback));
    // configuration of the observer:
    var config = {
      attributes: false,
      childList: true,
      characterData: true,
      subtree: true
    };

    // pass in the target node, as well as the observer options
    tempDiv.observer.observe(tempDiv, config);

  }

}



function pasteMutationObserver(callback) {

  document.getElementById("id_tempDiv_paste_editor").observer.disconnect();
  delete document.getElementById("id_tempDiv_paste_editor").observer;

  if (callback) {
    //return the copied dom tree to the supplied callback.
    //copy to avoid closures.
    callback.apply(document.getElementById("id_tempDiv_paste_editor").cloneNode(true));
  }
  document.body.removeChild(document.getElementById("id_tempDiv_paste_editor"));

}

function pasteCallBack() {
  //paste the content into the element.
  restoreSelection(document.getElementById("target_paste_element"), savedCaret);
  delete savedCaret;

  //edit the copied content by slicing
  pasteHtmlAtCaret(this.innerHTML.slice(3), false, true);
}


saveSelection = function(containerEl) {
  if (containerEl == document.activeElement) {
    var range = window.getSelection().getRangeAt(0);
    var preSelectionRange = range.cloneRange();
    preSelectionRange.selectNodeContents(containerEl);
    preSelectionRange.setEnd(range.startContainer, range.startOffset);
    var start = preSelectionRange.toString().length;

    return {
      start: start,
      end: start + range.toString().length
    };
  }
};

restoreSelection = function(containerEl, savedSel) {
  containerEl.focus();
  var charIndex = 0,
    range = document.createRange();
  range.setStart(containerEl, 0);
  range.collapse(true);
  var nodeStack = [containerEl],
    node, foundStart = false,
    stop = false;

  while (!stop && (node = nodeStack.pop())) {
    if (node.nodeType == 3) {
      var nextCharIndex = charIndex + node.length;
      if (!foundStart && savedSel.start >= charIndex && savedSel.start <= nextCharIndex) {
        range.setStart(node, savedSel.start - charIndex);
        foundStart = true;
      }
      if (foundStart && savedSel.end >= charIndex && savedSel.end <= nextCharIndex) {
        range.setEnd(node, savedSel.end - charIndex);
        stop = true;
      }
      charIndex = nextCharIndex;
    } else {
      var i = node.childNodes.length;
      while (i--) {
        nodeStack.push(node.childNodes[i]);
      }
    }
  }

  var sel = window.getSelection();
  sel.removeAllRanges();
  sel.addRange(range);
}

function pasteHtmlAtCaret(html, returnInNode, selectPastedContent) {
  //function written by Tim Down

  var sel, range;
  if (window.getSelection) {
    // IE9 and non-IE
    sel = window.getSelection();
    if (sel.getRangeAt && sel.rangeCount) {
      range = sel.getRangeAt(0);
      range.deleteContents();

      // Range.createContextualFragment() would be useful here but is
      // only relatively recently standardized and is not supported in
      // some browsers (IE9, for one)
      var el = document.createElement("div");
      el.innerHTML = html;
      var frag = document.createDocumentFragment(),
        node, lastNode;
      while ((node = el.firstChild)) {
        lastNode = frag.appendChild(node);
      }
      var firstNode = frag.firstChild;
      range.insertNode(frag);

      // Preserve the selection
      if (lastNode) {
        range = range.cloneRange();
        if (returnInNode) {
          range.setStart(lastNode, 0); //this part is edited, set caret inside pasted node.
        } else {
          range.setStartAfter(lastNode);
        }
        if (selectPastedContent) {
          range.setStartBefore(firstNode);
        } else {
          range.collapse(true);
        }
        sel.removeAllRanges();
        sel.addRange(range);
      }
    }
  } else if ((sel = document.selection) && sel.type != "Control") {
    // IE < 9
    var originalRange = sel.createRange();
    originalRange.collapse(true);
    sel.createRange().pasteHTML(html);
    if (selectPastedContent) {
      range = sel.createRange();
      range.setEndPoint("StartToStart", originalRange);
      range.select();
    }
  }
}

div {
  border: 1px solid black;
  height: 50px;
  padding: 5px;
}

---

Many thanks to Tim Down See this post for the answer:

Get the pasted content on document on paste event