UK VAT Number Validation

UK VAT Number Validation added

Author: Matt Clements

example.html

@@ -111,6 +111,11 @@ <h2>Example of all features</h2>
                 <strong>Valid Swedish social security number yyyymmddXXXX</strong> <em>validate_swesc</em><br/>
                 <input data-validation="validate_swesc"/>
             </p>
+            
+            <p>
+                <strong>UK VAT Number</strong> <em>validate_ukvatnumber</em><br/>
+                <input name="4" data-validation="validate_ukvatnumber"/>
+            </p>
 
             <p>
                 <strong>Custom validation</strong>

jquery.formvalidator.js

@@ -400,6 +400,78 @@ jQueryFormUtils.validateSwedishMobileNumber = function(number) {
     return (/07[0-9{1}]/).test(begin) || (begin === '467' && number.substr(3, 1) === '0');
 };
 
+/**
+ * Validate that string is a UK VAT Number
+ * TODO: Extra Checking for other VAT Numbers (Other countries and UK Government/Health Authorities)
+ * Code Adapted from http://www.codingforums.com/showthread.php?t=211967
+ *
+ * @param {Number}
+ * @return {Boolean}
+ */
+jQueryFormUtils.validateUKVATNumber = function(number) {
+	number = number.replace(/[^0-9]/g, '');
+	
+	//Check Length
+	if(number.length < 9) {
+		return false;
+	}
+	
+	var valid = false;
+	
+	var VATsplit = [];
+	VATsplit = number.split("");
+	
+	var checkDigits = Number(VATsplit[7] + VATsplit[8]);  // two final digits as a number
+	
+	var firstDigit = VATsplit[0];
+	var secondDigit = VATsplit[1];
+	if ((firstDigit == 0) && (secondDigit >0)) {
+		return false;
+	}
+	
+	var total = 0;
+	for (var i=0; i<7; i++) {  // first 7 digits
+		total += VATsplit[i] * (8-i);  // sum weighted cumulative total
+	}
+	
+	var c = 0;
+	var i = 0;
+	
+	for (var m = 8; m>=2; m--) {
+		c += VATsplit[i] * m;
+		i++;
+	}
+	
+	// Traditional Algorithm for VAT numbers issued before 2010
+	
+	while (total > 0) {
+		total -= 97; // deduct 97 repeatedly until total is negative
+	}
+	total = Math.abs(total);  // make positive
+	
+	if (checkDigits == total) {
+		valid = true;
+	}
+	
+	// If not valid try the new method (introduced November 2009) by subtracting 55 from the mod 97 check digit if we can - else add 42
+	
+	if (!valid) {
+		total = total%97  // modulus 97  
+		
+		if (total >= 55) {
+			total = total - 55
+		} else {
+			total = total + 42
+		}
+		
+		if (total == checkDigits) {
+			valid = true;
+		}
+	}
+	
+	return valid;
+};
+
 /**
  * Is this a valid birth date YYYY-MM-DD
  *
@@ -781,6 +853,11 @@ jQueryFormUtils.validateInput = function(el, language, config, form) {
         else if (validationRules.indexOf('validate_spamcheck') > -1 && !jQueryFormUtils.simpleSpamCheck(value, validationRules)) {
             return language.badSecurityAnswer;
         }
+        
+        // UK VAT Number check
+        else if (validationRules.indexOf('validate_ukvatnumber') > -1 && !jQueryFormUtils.validateUKVATNumber(value)) {
+            return language.badUKVatAnswer;
+        }
 
         // Custom regexp validation
         if (validationRules.indexOf('validate_custom') > -1 && validationRules.indexOf('regexp/') > -1) {
@@ -835,7 +912,8 @@ jQueryFormUtils.LANG =  {
     badFloat : 'Incorrect float value',
     badCustomVal : 'You gave an incorrect answer',
     badInt : 'Incorrect integer value',
-    badSecurityNumber : 'Your social security number was incorrect'
+    badSecurityNumber : 'Your social security number was incorrect',
+    badUKVatAnswer : 'Incorrect UK VAT Number'
 };