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<!DOCTYPE html> <html> <body> <img id="myImg" src="/i/shanghai_lupu_bridge.jpg" alt="上海卢浦大桥" width="350" height="234"> <p>单击按钮以显示图像的替代文本。</p> <button onclick="myFunction()">试一试</button> <p id="demo"></p> <script> function myFunction() { var x = document.getElementById("myImg").alt; document.getElementById("demo").innerHTML = x; } </script> </body> </html>