纯javascript字符串截取函数代码

```var getmindstr = function (con, l, r, ll, rl) {
  //--获取字符中间的字符,ll,rl是否最后一个匹配
  var lp, rp, cp;
  lp =
    l == ""
      ? 0
      : ll == false
        ? (lp = con.indexOf(l))
        : (lp = con.lastIndexOf(l));
  if (lp == -1) return "";
  lp = lp + l.length;
  rp =
    r == ""
      ? con.length
      : rl == false
        ? con.indexOf(r, lp)
        : (rp = con.lastIndexOf(r));
  if (rp == -1) return "";
  cp = rp - lp;
  if (cp < 0) return "";
  return con.substr(lp, cp);
}