js的replace的用法

 <script language="javascript">
   var strM = "javascript is a good script language";
   //在此我想将字母a替换成字母A
   alert(strM.replace("a","A"));

 </script>

 //结果，它只替换了首字母。但如果加上正则表达式结果就不一样了！replace()支持正则表达式，它可以按照正则表达式的规则匹配字符或字符串，然后给予替换！

 <script language="javascript">
    var strM = "javascript is a good script language";
 //在此我想将字母a替换成字母A
    alert(strM.replace(/a/,"A"));
 </script> 

 //但是结果还是没有更改，稍加修改就OK了。

 <script language="javascript">
    var strM = "javascript is a good script language";
 //在此将字母a全部替换成字母A,当正则表达式有"g"标志时，代表将处理整个字符串
    alert(strM.replace(/a/g,"A"));
 </script>