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<!DOCTYPE html> <html> <body> <h2>JavaScript 字符串方法</h2> <p>如果找不到文本，indexOf() 和 lastIndexOf() 都会返回 -1：</p> <p id="demo"></p> <script> var str = "Please locate where 'locate' occurs!"; var pos = str.indexOf("John"); document.getElementById("demo").innerHTML = pos; </script> </body> </html>