javascript - I cant get this script to work in IE, what am I doing wrong -

i wanting use script , finding wont work in internet explorer. t work in other tested browsers. thanks

<form name = "myform">     <b>to find if service area,<br> please enter postcode</b><br> <input type = "text" name = "zip" size = "4" maxlength = "4" onchange = "checkzip()"> </form>  <script type = "text/javascript">     function checkzip() {          var z = document.myform.zip;         var zv = z.value;         if (!/^\d{4}$/.test(zv)) {             alert ("please enter valid postcode");             document.myform.zip.value = "";             myfield = z;  // note myfield must global variable             settimeout('myfield.focus(); myfield.select();' , 10);  // fix bug in firefox             return false;         }          var codes = [4000,4005,4006,4007,4008,4009,4010,4011,4012,4013,4014,4030,4051,4059,4064,                      4065,4066,4075,4101,4102,4103,4104,4105,4106,4107,4108,4109,4110,4111,4112,                      4113,4114,4115,4116,4117,4119,4120,4121,4122,4123,4127,4128,4151,4152,4153,                      4154,4155,4156,4157,4158,4159,4160,4161,4163,4164,4169,4170,4171,4172,4173,                      4174,4178,4179];         // add many zip codes like, separated commas (no comma @ end)         var found = false;         (var i=0; i<codes.length; i++) {             if (zv == codes[i]) {                 found = true;                 break;             }         }          if (!found) {             alert ("the post code " + zv + " not in our database, please call 1300 736 979 check , see if can you.");             document.myform.zip.value = "";             return false;         }         else {             alert ("yes, post code covered our business");         }     }  </script>