Angular 1.x directive for handling number input

number-input.js

angular
  .module('angular-number-input', [])
  .directive('number-input', NumberInput);

function NumberInput() {
  return {
    restrict: 'A',
    require: 'ngModel',
    link: function (scope, element, attrs, ngModel) {
      scope.$watch(attrs.ngModel, watchValue);

      function watchValue(newValue, oldValue) {
        if (newValue === "" || newValue === oldValue) return;

        var strValue = new String(newValue);
        var parts = splitNumber(strValue);

        if (!parts) return updateViewValue(oldValue || '');

        var value = [
          allowNegative() && parts[1],
          parts[2],
          allowDecimal() && parts[3],
          allowDecimal() && parts[4] && trimDecimals(parts[4], parseInt(attrs.decimalUpto, 10))
        ].filter(identity).join('');

        return strValue !== value && updateViewValue(value);
      }

      function identity(o) { return o }

      function splitNumber(num) { return num.match(/^(-?)([0-9]+)?([,|\.])?([0-9]+)?$/) }

      function allowNegative() { return attrs.allowNegative !== 'false' }

      function allowDecimal() { return attrs.allowDecimal !== 'false' }

      function trimDecimals(str, max) { return str.slice(0, max || str.length) }

      function updateViewValue(value) {
        ngModel.$setViewValue(value);
        ngModel.$render();
      }
    }
  };
}