Set the FileList of <input type="file"> to arbitrary File objects

set-input-fileList.js

// @source https://embed.plnkr.co/HpBkr4/

// some data or data from file input 
const data = [
	new File(["a"], "a.txt"), new File(["b"], "b.txt")
];
// https://github.com/w3c/clipboard-apis/issues/33
class _DataTransfer {
	constructor() {
		return new ClipboardEvent("").clipboardData || new DataTransfer();
	}
}

const input = document.createElement("input");
input.type = "file";
input.name = "files[]";
input.multiple = true;
input.id = "files";

const dt = new _DataTransfer();
for (let file of data) {
  dt.items.add(file)
}

if (dt.files.length) {
  input.files = dt.files;
}