<html><body><h1>演示如何访问文件上传按钮</h1><input type="file" id="myFile"><p>单击“试一试”按钮禁用文件上传按钮。</p><button onclick="myFunction()">试一试</button><script>function myFunction() { var x = document.getElementById("myFile"); x.disabled = true;}</script></body></html>