Angular Form Validation

validation-form.html

<form id="addForm" name="addForm" novalidate>
    <label>Category:</label>
    <select ng-model="expense.category" ng-options="category for category in categories"></select>
    <label>Amount:</label>
    <input required type="number" ng-model="expense.amount"></input>
    <label>Description:</label>
    <input type="text" ng-pattern="/^[a-zA-Z 0-9]*$/" ng-model="expense.description"></input>
    <button ng-disabled="addForm.$pristine || addForm.$dirty && addForm.$invalid" ng-click="submit()">Submit</button>
</form>