validating a field + regular expression

hi experts

I have a function like

var validateCurrency = function(currency){

if currency is not alphabets and currency is not 3 characters long

alert('incorrect currency');


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Is there a regular expression to validate
if currency is not alphabets and currency is not 3 characters long

In my case currency can have values like

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Shaun KlineLead Software EngineerCommented:
You could do a not match:
if(!<your string>.match("[a-zA-Z]{3}"))
royjaydAuthor Commented:
but it doesnt look like its working
i have

                         alert('error');  //doesnt come here if currencyString is RRED

any idea what i am doing wrong.
Test page :
var isCurrency = function(str) {
      return /^[a-z]{3}$/gi.test(str);

if( ! isCurrency("euR") ) {
      alert('error euR');
if( ! isCurrency("RRED") ) {
      alert('error RRED');

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