index.html

﻿<!DOCTYPE html>
<html>
<head>
    <title>Post Repro</title>
    <script>
	document.addEventListener('DOMContentLoaded', ()=> {
		document.querySelector('#test').addEventListener('click', testFunction);
		document.querySelector('#test2').addEventListener('click', testFunction2);
	});
	function testFunction(e) {
	    var formData = new FormData();
		const file_input = document.querySelector('#files');
		formData.append("myFile", file_input.files[0]);
		var request = new XMLHttpRequest();
		request.open("POST", "./");
		request.send(formData);
	}
	function testFunction2(e) {
		const myForm = document.querySelector('#myForm');
		var formData = new FormData(myForm);
		var request = new XMLHttpRequest();
		request.open("POST", "./");
		request.send(formData);
	}
	</script>
</head>
<body bgcolor="#E6E6FA">
    <div>Pick a file</div>
	<form id="myForm" method="post" target="_blank">
	<input id="files" type="file" multiple="">
	<input id="test" type="button" value="Test">
	<input id="test2" type="button" value="Test (using Form)">
	</form>
</body>

</html>