filters on ng-model in an input

The question:

I have a text input and I don’t want to allow users to use spaces, and everything typed will be turned into lowercase.

I know I’m not allowed to use filters on ng-model eg.

ng-model='tags | lowercase | no_spaces'

I looked at creating my own directive but adding functions to $parsers and $formatters didn’t update the input, only other elements that had ng-model on it.

How can I change the input of that I’m currently typing in?

I’m essentially trying to create the ‘tags’ feature that works just like the one here on StackOverflow.

The Solutions:

Below are the methods you can try. The first solution is probably the best. Try others if the first one doesn’t work. Senior developers aren’t just copying/pasting – they read the methods carefully & apply them wisely to each case.

Method 1

I believe that the intention of AngularJS inputs and the ngModel direcive is that invalid input should never end up in the model. The model should always be valid. The problem with having invalid model is that we might have watchers that fire and take (inappropriate) actions based on invalid model.

As I see it, the proper solution here is to plug into the $parsers pipeline and make sure that invalid input doesn’t make it into the model. I’m not sure how did you try to approach things or what exactly didn’t work for you with $parsers but here is a simple directive that solves your problem (or at least my understanding of the problem):

app.directive('customValidation', function(){
   return {
     require: 'ngModel',
     link: function(scope, element, attrs, modelCtrl) {

       modelCtrl.$parsers.push(function (inputValue) {

         var transformedInput = inputValue.toLowerCase().replace(/ /g, ''); 

         if (transformedInput!=inputValue) {

         return transformedInput;         

As soon as the above directive is declared it can be used like so:

<input ng-model="sth" ng-trim="false" custom-validation>

As in solution proposed by @Valentyn Shybanov we need to use the ng-trim directive if we want to disallow spaces at the beginning / end of the input.

The advantage of this approach is 2-fold:

  • Invalid value is not propagated to the model
  • Using a directive it is easy to add this custom validation to any input without duplicating watchers over and over again

Method 2

I would suggest to watch model value and update it upon chage:

The only interesting issue is with spaces: In AngularJS 1.0.3 ng-model on input automatically trims string, so it does not detect that model was changed if you add spaces at the end or at start (so spaces are not automatically removed by my code). But in 1.1.1 there is ‘ng-trim’ directive that allows to disable this functionality (commit). So I’ve decided to use 1.1.1 to achieve exact functionality you described in your question.

Method 3

A solution to this problem could be to apply the filters on controller side :

$scope.tags = $filter('lowercase')($scope.tags);

Don’t forget to declare $filter as dependency.

Method 4

If you are using read only input field, you can use ng-value with filter.

for example:

ng-value="price | number:8"

Method 5

Use a directive which adds to both the $formatters and $parsers collections to ensure that the transformation is performed in both directions.

See this other answer for more details including a link to jsfiddle.

Method 6

I had a similar problem and used


in my handler I call a method of the objectInScope to modify itself correctly (coarse input). In the controller I have initiated somewhere that

$scope.objectInScope = myObject; 

I know this doesn’t use any fancy filters or watchers… but it’s simple and works great. The only down-side to this is that the objectInScope is sent in the call to the handler…

Method 7

If you are doing complex, async input validation it might be worth it to abstract ng-model up one level as part of a custom class with its own validation methods.



  <label for="a">input a</label>
    ng-class="{'is-valid': == true, 'is-invalid': == false}"
    placeholder="{{ === false ? : ''}}"
    id="a" />

  <label for="b">input b</label>
    ng-class="{'is-valid': == true, 'is-invalid': == false}"
    placeholder="{{ === false ? : ''}}"
    id="b" />



(function() {

  const _ = window._;

    .module('app', [])
    .directive('componentLayout', layout)
    .controller('Layout', ['Validator', Layout])
    .factory('Validator', function() { return Validator; });

  /** Layout controller */

  function Layout(Validator) { = {
      a: new Validator({title: 'input a'}),
      b: new Validator({title: 'input b'})

  /** layout directive */

  function layout() {
    return {
      restrict: 'EA',
      templateUrl: 'layout.html',
      controller: 'Layout',
      controllerAs: 'vm',
      bindToController: true

  /** Validator factory */  

  function Validator(config) {
    this.model = null;
    this.isValid = null;
    this.title = config.title;

  Validator.prototype.isEmpty = function(checkName) {
    return new Promise((resolve, reject) => {
      if (/^s+$/.test(this.model) || this.model.length === 0) {
        this.isValid = false;
        this.warning = `${this.title} cannot be empty`;
        reject(_.merge(this, {test: checkName}));
      else {
        this.isValid = true;
        resolve(_.merge(this, {test: checkName}));

   * @memberof Validator
   * @param {array} checks - array of strings, must match defined Validator class methods

  Validator.prototype.validate = function(checks) {
      .all( => this[check](check)))
      .then(res => { console.log('pass', res)  })
      .catch(e => { console.log('fail', e) })


Method 8

You can try this

$scope.$watch('tags ',function(){

    $scope.tags = $filter('lowercase')($scope.tags);


Method 9

I came here to look for a solution that would actively change an input text and mask it with * for all but last 4 digits as we type. This is achieved by $formatters

eg: Account Num input box: 1234567890AHSB1 should display in the input box as **********AHSB

Answer is just a slight variation of that given by @pkozlowski.opensource above.

angular.module('myApp').directive('npiMask', function() {
  return {
    require: 'ngModel',
    link: function($scope, element, attrs, modelCtrl) {
      modelCtrl.$formatters.push(function(inputValue) {
        var transformedInput = inputValue.toString().replace(/.(?=.{4,}$)/g, '*');
        if (transformedInput !== inputValue) {
        return transformedInput;
 label="{{'LOAN_REPAY.ADD_LOAN.ACCOUNT_NUM_LABEL' | translate}}" 

All methods was sourced from or, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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