

这样一来,解决问题的思路就出来了:
下面用一个Demo展示具体的代码实现用FormData将文件发送到一个php:
<html>
<head>
<title>Upload</title>
<meta charset="utf-8">
</head>
<body>
<input id="file-input" type="file">
<script>
var input = document.getElementById('file-input');
input.onchange = function () {
var data = new FormData();
data.append('file', input.files[0]);
var request = new XMLHttpRequest();
request.open('POST', './upload.php');
request.send(data);
};
</script>
</body>
</html>