Australian Postcode to State - Demo https://jsfiddle.net/7o772r4s/4/

post2state.js

// Data from https://en.wikipedia.org/wiki/Postcodes_in_Australia
function postcodeToState(input) {
	// Convert.
  var postcode = parseInt(input);
  
  // Is valid.
  if (isNaN(postcode) || postcode > 9999 || postcode < 100) {
  	return "Invalid postcode";
  }
  
  // Handle edge states
  switch (postcode) {
  	case 0872:
    	return "QLD, SA, WA";
    case 2540:
    case 2620:
    case 2611:
    
    	return "ACT, NSW";
    case 2611:
    case 3500:
    case 3585:
    case 3586:
    case 3644:
    case 3707:
    	return "NSW";
    case 2406:
    case 4380:
    case 4377:
    	return "NSW, QLD";
    case 3691:
    	return "NSW, VIC";
    // Islands
    case 2889:
    	return "Norfolk Island";
    case 6798:
    	return "Christmas Island";
    case 6799:
    	return "Cocos (Keeling) Islands";
    // Antarctica
    case 7151:
    	return "Antarctica";
    default:
    	break;
  }
  
  // Blocks.
	if ((postcode >= 1000 && postcode <= 2599) || 
  (postcode >= 2619 && postcode <= 2899) || 
  (postcode >= 2921 && postcode <= 2999)) {
  	return "NSW";
  } else if ((postcode >= 0200 && postcode <= 0299) || 
  (postcode >= 2600 && postcode <= 2618) || 
  (postcode >= 2900 && postcode <= 2920)) {
  	return "ACT";
  } else if ((postcode >= 3000 && postcode <= 3999) || 
  (postcode >= 8000 && postcode <= 8999)) {
  	return "VIC";
  } else if ((postcode >= 4000 && postcode <= 4999) || 
  (postcode >= 9000 && postcode <= 9999)) {
  	return "QLD";
  } else if ((postcode >= 5000 && postcode <= 5999)) {
  	return "SA";
  } else if ((postcode >= 7000 && postcode <= 7999)) {
  	return "TAS";
  } else if ((postcode >= 0800 && postcode <= 0999)) {
  	return "NT";
  }

  return "Unknown"
}