代码如下：
<SCRIPT LANGUAGE="JavaScript"> <!-- Begin function replaceChars(entry) { out = "a"; // 要替代的字母 add = "z"; // 替换后的字母 temp = "" + entry; while (temp.indexOf(out)>-1) { pos= temp.indexOf(out); temp = "" + (temp.substring(0, pos) + add + temp.substring((pos + out.length), temp.length)); } document.subform.text.value = temp; } // End --> </script> <center> <form name="subform"> <input type=text name=text size=40 value="abcdabcd"><br> <input type=button name=action value="Done!" onClick="replaceChars(document.subform.text.value);"> </form> </center>