js 指定分隔符连接数组元素join()

示例：
<script type="text/javascript">
  var myarr = new Array(3);
  myarr[0] = "I";
  myarr[1] = "Love";
  myarr[2] = "JS";
  document.write(myarr.join());
</script>
结果：
I,Love,JS