Thank you. I solved the problem thanks to you.
I made a html component in form like below.
When copy and paste an image from clipboard, it will be uploaded in vault.
and the uploaded file will be Item's image property.
<div>
<img src="" id="pastedImage">
</div>
<script>
document.onpaste = function(event) {
var items = event.clipboardData.items;
console.log(JSON.stringify(items)); // will give you the mime types
var blob = items[0].getAsFile();
var reader = new FileReader();
reader.onload = function(event) {
console.log(event.target.result);
document.querySelector('#pastedImage').src = event.target.result;
var file = new File([blob],'test.png',{type:"image/png"});
var newFile = aras.newFileItem(file);
var fileId = newFile.getAttribute("id");
var fileItem = aras.IomInnovator.newItem();
fileItem.loadAML(newFile.xml);
fileItem = fileItem.apply();
window.handleItemChange("_paste_image","vault:///?fileId="+fileId);
}; // data url
reader.readAsDataURL(blob);
}
</script>