Displaying Form Validation Errors with the Twitter Bootstrap framework


You wish to display form validation errors but the form is styled using Twitter Bootstrap.


When using the .horizontal-form class Twitter Bootstrap uses div elements to structure label, input fields and help messages into groups. The group div has the class control-group and the actual controls are further nested in another div element with the CSS class controls. Twitter Bootstrap shows a nice validation status when adding the CSS class error on the div with the control-group class.

Let us start with the form:

<div ng-controller="User">
  <form name="form" ng-submit="submit()" novalidate>

    <div class="control-group" ng-class="error('firstname')">
      <label class="control-label" for="firstname">Firstname</label>
      <div class="controls">
        <input id="firstname" name="firstname" type="text"
          ng-model="user.firstname" placeholder="Firstname" required/>
        <span class="help-block"
          ng-show="form.firstname.$invalid && form.firstname.$dirty">
          Firstname is required

    <div class="control-group" ng-class="error('lastname')">
      <label class="control-label" for="lastname">Lastname</label>
      <div class="controls">
        <input id="lastname" name="lastname" type="text"
          ng-model="user.lastname" placeholder="Lastname" required/>
        <span class="help-block"
          ng-show="form.lastname.$invalid && form.lastname.$dirty">
          Lastname is required

    <div class="control-group">
      <div class="controls">
        <button ng-disabled="form.$invalid" class="btn">Submit</button>

Note that we use the ng-class directive on the control-group div. So let’s look at the controller implementation of the error function:

app.controller("User", function($scope) {
  // ...
  $scope.error = function(name) {
    var s = $scope.form[name];
    return s.$invalid && s.$dirty ? "error" : "";

The error function gets the input name attribute passed as a string and checks for the $invalid and $dirty flags to return either the error class or a blank string.

You can find the complete example on github.


Again we check both the invalid and dirty flags because we only show the error message in case the user has actually changed the form. Note that this ng-class function usage is pretty typical in Angular since expressions do not support ternary checks.