js replace 全局替换的操作方法

<script language="javascript">
var strM = "这是要被替换的字符串啊啊！";
//在此我想将字母a替换成字母A
alert(strM.replace("啊","额"));
</script>

<script type="text/javascript" language="javascript">
var s = "这是要被替换的字符换啊啊！";
alert(s);
alert(s.replace(/啊/g, "额"));

<script>
var ch = "变量";
var reg = "/"+ch+"/g";
var str = "这是一个变量，这是一个变量";
var val = str.replace(eval(reg),"替换");
alert(val);
</script>

<script>
var ch = "/";
var str = "这是一/个变量，这是一个变量";
var val = str .replace(new RegExp(ch,'g'),"b");
alert(val);
</script>