Avoid type="number" in AngularJS

  • Written

The other day I got hit by a peculiar bug in Angular. Using type="number" on an input element wouldn’t do any number validation. On top of this, when I entered an invalid number the only validation failing was required.

After a little research, it turned out to be a “feature” of blocking access to the value attribute when it’s an invalid number. Not all browsers follow the complete spec, so I found this was working in Firefox. Back in Chrome however, it was failing. You can even test this in the AngularJS documentation by typing an invalid number in the demo and looking at the error message.

Custom Type Directive

var app = angular.module('myApp', []);

/**
 * Provide custom type validation for input elements. Certain type attributes
 * don't work consistenty cross-browser, so this is a required workaround.
 * Looking at you, webkit and `type="number"`.
 *
 * ```html
 * <input
 *   ng-model=""
 *   app-type="">
 * ```
 */
app.directive('appType', function () {
  return {
    require: 'ngModel',
    link: function (scope, elem, attrs, ctrl) {
      // Custom number validation logic.
      if (attrs.appType === 'number') {
        return ctrl.$parsers.push(function (value) {
          var valid = value == null || isFinite(value);

          ctrl.$setValidity('number', valid);

          return valid && value != null ? Number(value) : undefined;
        });
      }
    }
  };
});

The code above adds a new custom directive that requires ngModel. Requiring ngModel provides us with the ngModelController. Using the controller we can access some useful methods, including model input parsing and validity - which makes up the bulk of our validation logic.

When the type is number, we push a custom parser onto the stack. Our parser goes on the end and will run after any other parsers, allowing us to keep the required directive in tact. The validity itself checks if the value is empty (null or undefined) or that it’s a valid JavaScript number. Valid “JavaScript number” is important to note, since this will allow the most comprehensive check including integers, floats, negative and positive notation, but also other notations such as 0x1e5 and 1e5.

Validity gets set next and based on the result we’ll coerce the value into a number. By doing number coercion, the model will correctly receive the number instead of the string representation. We want to avoid coercing empty values (null and undefined) however, which will come out as 0 and NaN respectfully.

Recreating min and max directives

var app = angular.module('myApp', []);

/**
 * Provide minimum number validation for any input.
 *
 * ```html
 * <input
 *   ng-model=""
 *   app-min="">
 * ```
 */
app.directive('appMin', function () {
  return {
    require: 'ngModel',
    link: function (scope, elem, attrs, ctrl) {
      return ctrl.$parsers.push(function (value) {
        var valid = value == null || Number(value) >= Number(attrs.appMin);

        ctrl.$setValidity('min', valid);

        return valid ? value : undefined;
      });
    }
  };
});

Recreating the min directive is trivial and we can easily make it work for any input. The above validation does the null check again, which will make an empty input element valid. This is important since we don’t want to provide unnecessary validation and bundle the required directives job into ours.

Next it’s just a process of coercing both the value and attribute into numbers and comparing the values. If either are NaN, validation will fail. This provides some form of ensuring we have numbers only, but won’t do any number coerce to the model. Finally, we return either the value or undefined if validation failed.

Unit Testing

Unit testing the functionality was straightforward enough, so I won’t provide all the code used. A couple of things worth mentioning though is how to compile the templates for testing and set the values for validation.

it('...', function () {
  inject(function ($compile, $rootScope) {
    var $scope = $rootScope.$new();

    $scope.model = {};

    var $element = $compile(
      '<form name="form">' +
      '  <input name="num" ng-model="model.value" app-type="number">' +
      '</form>'
    )($scope);

    // Set the value to what you want to test.
    $scope.form.num.$setViewValue('10');

    // Check the model is what you expect and check validation.
    $scope.model.value.should.equal(10);
    $scope.form.num.$invalid.should.be.false;
  });
});

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