Monday, August 18, 2014

AngularJS validation messages using ngMessages

As you know AngularJS provides several validation attributes such as required, minimum length, pattern etc which simplify the form validation. But showing the validation messages is a big pain (up to version 1.3). We have to write a bunch of ng-if statements to show the proper error message and this get much more complex than the actual validation.

AngularJS reduces this pain of showing validation messages using ngMessages directive. The ngMessages internally works like a switch statement, it will accept an object and based on the values of this object, ngMessages shows the corresponding message. This can be better demonstrated with the below example:

Let’s say we have the below javascript object

    var messages = {
        required: false,
        minlength: false,
        maxlength: false,
        email: true

As you see this object contains a set of properties out of which email is true. Now we will pass this object to the ngMessages directive as mentioned below

<div ng-messages='vm.messages'>
    <div ng-message="required">This field is required</div>
    <div ng-message="minlength">This field is too short</div>
    <div ng-message="maxlength">This field is too long</div>
    <div ng-message="email">This field has an invalid email address</div>

As expected ngMessages shows the message corresponding to the email as it’s value is true.
In the actual scenario, instead of our custom object, we will pass the angular’s error attribute as shown below:

<div ng-messages='loginForm.username.$error>

The ngMessages based on the angular’s error attribute shows the message. Here is the full code on using the ngMessages directive

    <div class="form-group" ng-class="{'has-error': loginForm.username.$invalid && vm.isFormSubmitted(loginForm.username) }">
        <label for="username" class="col-sm-2 control-label">Username</label>
        <div class="col-sm-3">
            <input type="text" class="form-control" name="username" ng-model="vm.model.UserName" required autofocus>
            <div class="error-messages" ng-messages="loginForm.username.$error" ng-if="vm.isFormSubmitted(loginForm.username)">
                <div ng-message="required">Username is required</div>

In my next blog I will go more detail on the above code. For now let’s assume ngMessage directive acts like a switch statement.

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