function currencyFilter($locale) {
  var formats = $locale.NUMBER_FORMATS;
  return function(amount, currencySymbol, fractionSize) {
    if (isUndefined(currencySymbol)) {
      currencySymbol = formats.CURRENCY_SYM;
    }

    if (isUndefined(fractionSize)) {
      fractionSize = formats.PATTERNS[1].maxFrac;
    }

    // If the currency symbol is empty, trim whitespace around the symbol
    var currencySymbolRe = !currencySymbol ? /\s*\u00A4\s*/g : /\u00A4/g;

    // if null or undefined pass it through
    return (amount == null)
        ? amount
        : formatNumber(amount, formats.PATTERNS[1], formats.GROUP_SEP, formats.DECIMAL_SEP, fractionSize).
            replace(currencySymbolRe, currencySymbol);
  };
}
@ngdoc filter
@name currency
@kind function

@description
Formats a number as a currency (ie $1,234.56). When no currency symbol is provided, default
symbol for current locale is used.

@param {number} amount Input to filter.
@param {string=} symbol Currency symbol or identifier to be displayed.
@param {number=} fractionSize Number of decimal places to round the amount to, defaults to default max fraction size for current locale
@returns {string} Formatted number.


@example
   <example module="currencyExample" name="currency-filter">
     <file name="index.html">
       <script>
         angular.module('currencyExample', [])
           .controller('ExampleController', ['$scope', function($scope) {
             $scope.amount = 1234.56;
           }]);
       </script>
       <div ng-controller="ExampleController">
         <input type="number" ng-model="amount" aria-label="amount"> <br>
         default currency symbol ($): <span id="currency-default">{{amount | currency}}</span><br>
         custom currency identifier (USD$): <span id="currency-custom">{{amount | currency:"USD$"}}</span><br>
         no fractions (0): <span id="currency-no-fractions">{{amount | currency:"USD$":0}}</span>
       </div>
     </file>
     <file name="protractor.js" type="protractor">
       it('should init with 1234.56', function() {
         expect(element(by.id('currency-default')).getText()).toBe('$1,234.56');
         expect(element(by.id('currency-custom')).getText()).toBe('USD$1,234.56');
         expect(element(by.id('currency-no-fractions')).getText()).toBe('USD$1,235');
       });
       it('should update', function() {
         if (browser.params.browser === 'safari') {
           // Safari does not understand the minus key. See
           // https://github.com/angular/protractor/issues/481
           return;
         }
         element(by.model('amount')).clear();
         element(by.model('amount')).sendKeys('-1234');
         expect(element(by.id('currency-default')).getText()).toBe('-$1,234.00');
         expect(element(by.id('currency-custom')).getText()).toBe('-USD$1,234.00');
         expect(element(by.id('currency-no-fractions')).getText()).toBe('-USD$1,234');
       });
     </file>
   </example>