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<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>本教程(w3big.com)</title> </head> <body> <p id="demo">单击按钮显示指定值最后一次出现的位置。</p> <button onclick="myFunction()">点我</button> <script> function myFunction(){ var str="Hello planet earth, you are a great planet."; var n=str.lastIndexOf("planet"); document.getElementById("demo").innerHTML=n; } </script> </body> </html>