<!DOCTYPE html>
<html>
<body>
<div id="editor" contenteditable></div>
<script>
const editor = document.getElementById('editor');
editor.focus();

var dataTransfer = {};
editor.addEventListener('paste', (event) => {
    dataTransfer.types = Array.from(event.clipboardData.types);
    dataTransfer.files = Array.from(event.clipboardData.files);
    dataTransfer.items = Array.from(event.clipboardData.items).map(cloneItem);
});

function cloneItem(item) {
    return {
        kind: item.kind,
        type: item.type,
        file: item.getAsFile(),
    }
}

var imageElement;
function insertFileAsImage(file) {
    imageElement = document.createElement('img');
    imageElement.onload = () => window.webkit.messageHandlers.testHandler.postMessage('loaded');
    imageElement.src = URL.createObjectURL(file);
    document.body.appendChild(imageElement);
}

</script>
</body>
</html>