JS任意文件转base64

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<meta name="description" content="在线Base64生成转换小工具，可以实现任意文件转Base64 Data-URI编码，文件往页面中一拖即可。" />
<meta name="keywords" content="base64, FileReader, readAsDataURL, 文件" />
<meta name="author" content="谢勇彬，XYB" />
<title>任意文件转base64-直接拖进来</title>
<style>
    body { word-break: break-all; margin: 0 1em; min-height: 100vh; font-family: Consolas, "Andale Mono", "Lucida Console", "Lucida Sans Typewriter", Monaco, "Courier New", monospace; overflow: hidden;}
    .empty::before{position: absolute; font-size: 50px; content: '任意文件\A拖到这里'; white-space: pre; left: 50%; top: 50%; transform: translate(-50%,-50%); color: gray;}
</style>
</head>
<body class="empty">
<script>
    window.addEventListener("dragenter", function(event) { event.preventDefault(); }, false);
    window.addEventListener("dragover", function(event) { event.preventDefault(); }, false);
    window.addEventListener("drop", function(event) {
        var reader = new FileReader();
        reader.onload = function(e) {
            document.body.insertAdjacentHTML("afterBegin", '<p>' + e.target.result + '</p>');
            document.body.classList.remove('empty');
        };
        reader.readAsDataURL(event.dataTransfer.files[0]);
        event.preventDefault();
    }, false);
</script>

</body>
</html>