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<!DOCTYPE html> <html> <body> <p>单击按钮以显示基于时间的问候语：</p> <button onclick="myFunction()">试一试</button> <p id="demo"></p> <script> function myFunction() { var hour = new Date().getHours(); var greeting; if (hour < 18) { greeting = "日安"; } else { greeting = "晚安"; } document.getElementById("demo").innerHTML = greeting; } </script> </body> </html>