IP验证的js

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function checkip(ip)
    {
       var pcount = 0;
       var ip_length = ip.length;
       var ip_letters = "1234567890.";
       for (p=0; p < ip_length; p++)
       {
       var ip_char = ip.charAt(p);
       if (ip_letters.indexOf(ip_char) == -1)
       {
           return false;
       }
       }
       for (var u = 0; u < ip_length; u++) { (ip.substr(u,1) == ".") ? pcount++ : pcount; }
       if(pcount != 3) { return false; };
       firstp = ip.indexOf(".");
       lastp = ip.lastIndexOf(".");
       str1 = ip.substring(0,firstp);
       ipstr_tmp = ip.substring(0,lastp);
       secondp = ipstr_tmp.lastIndexOf(".");
       str2 = ipstr_tmp.substring(firstp+1,secondp);
       str3 = ipstr_tmp.substring(secondp+1,lastp);
       str4 = ip.substring(lastp+1,ip_length);
       if (str1 == '' || str2 == '' || str3 == '' || str4 == '') { return false; }
       if (str1.length > 3 || str2.length > 3 || str3.length > 3 || str4.length > 3) { return false; }
       if (str1 <= 0 || str1 > 255) { return false; }
       else if (str2 < 0 || str2 > 255) { return false; }
       else if (str3 < 0 || str3 > 255) { return false; }
       else if (str4 < 0 || str4 > 255) { return false; }