JavaScript FileReader API 完整指南：方法、属性、事件与常见问题处理

if (window.FileReader) {
 let reader = new FileReader();
} else {
 console.log('你的浏览器不支持读取文件');
}

<!DOCTYPE html>
<html class="no-js">
	<head>
		<meta charset="utf-8" />
		<meta http-equiv="X-UA-Compatible" content="IE=edge" />
		<title></title>
		<meta name="description" content="" />
		<meta name="viewport" content="width=device-width, initial-scale=1" />
		<link rel="stylesheet" href="" />
	</head>
 
	<body>
		<input type="file" id="myFile" />
		<script type="text/javascript">
			if (window.FileReader) {
				var reader = new FileReader();
			} else {
				console.log('你的浏览器不支持读取文件');
			}
			var myFile = document.querySelector('#myFile');
			myFile.onchange = function () {
				var file = myFile.files[0];
				reader.readAsDataURL(file);
				reader.onload = function () {
					var data = reader.result;   //base64形式的文件内容
				};
                reader.onerror = function(){
                    console.log('读取失败');
                    console.log(reader.error);
                }
			};
		</script>
	</body>
</html>

(1) java.net.URL url = TestScriptEngine.class.getClassLoader().getResource("a.js");
(2)//System.out.println(url.getPath().substring(1).replace("%20", " "));
(3)FileReader fileReader = new FileReader(url.getPath());