Angular JS. Validation.

form.html

<form data-ng-app="form-example" class="row form-horizontal" novalidate>
 <div class="control-group">
  <label class="control-label" for="inputEmail">Email</label>
  <div class="controls">
    <input type="email" id="inputEmail" placeholder="Email" data-ng-model="email" required>
    <div class="input-help">
      <h4>Invalid Email</h4>
    </div>
  </div>
 </div>
<div class="control-group">
  <label class="control-label" for="inputPassword">Password</label>
  <div class="controls">
    <input data-ng-model="password" class="immediate-help" password-validate required type="password" id="inputPassword" placeholder="Password">
    <div class="input-help">
      <h4>Password must meet the following requirements:</h4>
      <ul>
        <li data-ng-class="pwdHasLetter">At least <strong>one letter</strong></li>
        <li data-ng-class="pwdHasNumber">At least <strong>one number</strong></li>
        <li data-ng-class="pwdValidLength">At least <strong>8 characters long</strong></li>
      </ul>
    </div>
  </div>
 </div>
<div class="control-group">
  <div class="controls">
    <button type="submit" class="btn">Create Account</button>
    <button class="btn" disabled>Create Account</button>
  </div>
 </div>
</form>

validation.js

var app = angular.module('form-example', []);

app.directive('passwordValidate', function() {
    return {
        require: 'ngModel',
        link: function(scope, elm, attrs, ctrl) {
            ctrl.$parsers.unshift(function(viewValue) {

                scope.pwdValidLength = (viewValue && viewValue.length >= 8 ? 'valid' : undefined);
                scope.pwdHasLetter = (viewValue && /[A-z]/.test(viewValue)) ? 'valid' : undefined;
                scope.pwdHasNumber = (viewValue && /\d/.test(viewValue)) ? 'valid' : undefined;

                if(scope.pwdValidLength && scope.pwdHasLetter && scope.pwdHasNumber) {
                    ctrl.$setValidity('pwd', true);
                    return viewValue;
                } else {
                    ctrl.$setValidity('pwd', false);                    
                    return undefined;
                }

            });
        }
    };
});