如何用javascript来确定文本框中的逗号？？？？？？

Question

var s = "wo,ai,zhong,guo,";
alert(s.substring(0,s.length-1))

Answer 1

<script language="javascript">
var txt="a,b,c,";
alert(txt.replace(/,$/,""));
</script>

Answer 2

<script>
var txt = "a,b,c,";
var len = txt.length;
var str = txt.charAt(len-1); if(str == ",")
alert("true");
  else
alert("false");
</script>

Answer 3

var str = "a,b,c,d";
var arr = str.match(/,/gi);
alert(arr.length);

Answer 4

不好意思，没看清，这样：var str = "a,b,c,d,";
if(/,$/gi.test(str))
alert("最后有逗号");
else
alert("最后没逗号");