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# `ngMessages`

The `ngMessages` module provides enhanced support for displaying messages within templates (typically within forms or when rendering message objects that return key/value data). Instead of relying on JavaScript code and/or complex ng-if statements within your form template to show and hide error messages specific to the state of an input field, the `ngMessages` and `ngMessage` directives are designed to handle the complexity, inheritance and priority sequencing based on the order of how the messages are defined in the template.

Currently, the ngMessages module only contains the code for the `ngMessages`, `ngMessagesInclude` `ngMessage` and `ngMessageExp` directives.

# Usage

The `ngMessages` directive listens on a key/value collection which is set on the ngMessages attribute. Since the ngModel directive exposes an `$error` object, this error object can be used with `ngMessages` to display control error messages in an easier way than with just regular angular template directives.

    <form name="myForm">
      <label>
        Enter text:
        <input type="text" ng-model="field" name="myField" required minlength="5" />
      </label>
      <div ng-messages="myForm.myField.$error" role="alert">
        <div ng-message="required">You did not enter a field</div>
        <div ng-message="minlength, maxlength">
          Your email must be between 5 and 100 characters long
        </div>
      </div>
    </form>

Now whatever key/value entries are present within the provided object (in this case `$error`) then the ngMessages directive will render the inner first ngMessage directive (depending if the key values match the attribute value present on each ngMessage directive). In other words, if your errors object contains the following data:

    <!-- keep in mind that ngModel automatically sets these error flags -->
    myField.$error = { minlength : true, required : true };

Then the `required` message will be displayed first. When required is false then the `minlength` message will be displayed right after (since these messages are ordered this way in the template HTML code). The prioritization of each message is determined by what order they're present in the DOM. Therefore, instead of having custom JavaScript code determine the priority of what errors are present before others, the presentation of the errors are handled within the template.

By default, ngMessages will only display one error at a time. However, if you wish to display all messages then the `ng-messages-multiple` attribute flag can be used on the element containing the ngMessages directive to make this happen.

    <!-- attribute-style usage -->
    <div ng-messages="myForm.myField.$error" ng-messages-multiple>...</div>

    <!-- element-style usage -->
    <ng-messages for="myForm.myField.$error" multiple>...</ng-messages>

## Reusing and Overriding Messages

In addition to prioritization, ngMessages also allows for including messages from a remote or an inline template. This allows for generic collection of messages to be reused across multiple parts of an application.

    <script type="text/ng-template" id="error-messages">
      <div ng-message="required">This field is required</div>
      <div ng-message="minlength">This field is too short</div>
    </script>

    <div ng-messages="myForm.myField.$error" role="alert">
      <div ng-messages-include="error-messages"></div>
    </div>

However, including generic messages may not be useful enough to match all input fields, therefore, `ngMessages` provides the ability to override messages defined in the remote template by redefining them within the directive container.

    <!-- a generic template of error messages known as "my-custom-messages" -->
    <script type="text/ng-template" id="my-custom-messages">
      <div ng-message="required">This field is required</div>
      <div ng-message="minlength">This field is too short</div>
    </script>

    <form name="myForm">
      <label>
        Email address
        <input type="email"
               id="email"
               name="myEmail"
               ng-model="email"
               minlength="5"
               required />
      </label>
      <!-- any ng-message elements that appear BEFORE the ng-messages-include will
           override the messages present in the ng-messages-include template -->
      <div ng-messages="myForm.myEmail.$error" role="alert">
        <!-- this required message has overridden the template message -->
        <div ng-message="required">You did not enter your email address</div>

        <!-- this is a brand new message and will appear last in the prioritization -->
        <div ng-message="email">Your email address is invalid</div>

        <!-- and here are the generic error messages -->
        <div ng-messages-include="my-custom-messages"></div>
      </div>
    </form>

In the example HTML code above the message that is set on required will override the corresponding required message defined within the remote template. Therefore, with particular input fields (such email addresses, date fields, autocomplete inputs, etc...), specialized error messages can be applied while more generic messages can be used to handle other, more general input errors.

## Dynamic Messaging

ngMessages also supports using expressions to dynamically change key values. Using arrays and repeaters to list messages is also supported. This means that the code below will be able to fully adapt itself and display the appropriate message when any of the expression data changes:

    <form name="myForm">
      <label>
        Email address
        <input type="email"
               name="myEmail"
               ng-model="email"
               minlength="5"
               required />
      </label>
      <div ng-messages="myForm.myEmail.$error" role="alert">
        <div ng-message="required">You did not enter your email address</div>
        <div ng-repeat="errorMessage in errorMessages">
          <!-- use ng-message-exp for a message whose key is given by an expression -->
          <div ng-message-exp="errorMessage.type">{{ errorMessage.text }}</div>
        </div>
      </div>
    </form>

The `errorMessage.type` expression can be a string value or it can be an array so that multiple errors can be associated with a single error message:

    <label>
      Email address
      <input type="email"
             ng-model="data.email"
             name="myEmail"
             ng-minlength="5"
             ng-maxlength="100"
             required />
    </label>
    <div ng-messages="myForm.myEmail.$error" role="alert">
      <div ng-message-exp="'required'">You did not enter your email address</div>
      <div ng-message-exp="['minlength', 'maxlength']">
        Your email must be between 5 and 100 characters long
      </div>
    </div>

Feel free to use other structural directives such as ng-if and ng-switch to further control what messages are active and when. Be careful, if you place ng-message on the same element as these structural directives, Angular may not be able to determine if a message is active or not. Therefore it is best to place the ng-message on a child element of the structural directive.

    <div ng-messages="myForm.myEmail.$error" role="alert">
      <div ng-if="showRequiredError">
        <div ng-message="required">Please enter something</div>
      </div>
    </div>

## Animations

If the `ngAnimate` module is active within the application then the `ngMessages`, `ngMessage` and `ngMessageExp` directives will trigger animations whenever any messages are added and removed from the DOM by the `ngMessages` directive.

Whenever the `ngMessages` directive contains one or more visible messages then the `.ng-active` CSS class will be added to the element. The `.ng-inactive` CSS class will be applied when there are no messages present. Therefore, CSS transitions and keyframes as well as JavaScript animations can hook into the animations whenever these classes are added/removed.

Let's say that our HTML code for our messages container looks like so:

    <div ng-messages="myMessages" class="my-messages" role="alert">
      <div ng-message="alert" class="some-message">...</div>
      <div ng-message="fail" class="some-message">...</div>
    </div>

Then the CSS animation code for the message container looks like so:

    .my-messages {
      transition:1s linear all;
    }
    .my-messages.ng-active {
      // messages are visible
    }
    .my-messages.ng-inactive {
      // messages are hidden
    }

Whenever an inner message is attached (becomes visible) or removed (becomes hidden) then the enter and leave animation is triggered for each particular element bound to the `ngMessage` directive.

Therefore, the CSS code for the inner messages looks like so:

    .some-message {
      transition:1s linear all;
    }

    .some-message.ng-enter {}
    .some-message.ng-enter.ng-enter-active {}

    .some-message.ng-leave {}
    .some-message.ng-leave.ng-leave-active {}

Click here to learn how to use JavaScript animations or to learn more about ngAnimate.

## Installation

First include `angular-messages.js` in your HTML:

    <script src="angular.js">
    <script src="angular-messages.js">

You can download this file from the following places:

- Google CDN
  e.g. `//ajax.googleapis.com/ajax/libs/angularjs/X.Y.Z/angular-messages.js`
- Bower
  e.g.

      bower install angular-messages@X.Y.Z

- code.angularjs.org
  e.g.

      "//code.angularjs.org/X.Y.Z/angular-messages.js"

where X.Y.Z is the AngularJS version you are running.

Then load the module in your application by adding it as a dependent module:

    angular.module('app', ['ngMessages']);

With that you're ready to get started!

## Module Components

### Directive

Name | Description
--- | ---
ngMessages | `ngMessages` is a directive that is designed to show and hide messages based on the state of a key/value object that it listens on. The directive itself complements error message reporting with the `ngModel` $error object (which stores a key/value state of validation errors).
ngMessagesInclude | `ngMessagesInclude` is a directive with the purpose to import existing ngMessage template code from a remote template and place the downloaded template code into the exact spot that the ngMessagesInclude directive is placed within the ngMessages container. This allows for a series of pre-defined messages to be reused and also allows for the developer to determine what messages are overridden due to the placement of the ngMessagesInclude directive.
ngMessage | `ngMessage` is a directive with the purpose to show and hide a particular message. For `ngMessage` to operate, a parent `ngMessages` directive on a parent DOM element must be situated since it determines which messages are visible based on the state of the provided key/value map that `ngMessages` listens on.
ngMessageExp | `ngMessageExp` is a directive with the purpose to show and hide a particular message. For `ngMessageExp` to operate, a parent `ngMessages` directive on a parent DOM element must be situated since it determines which messages are visible based on the state of the provided key/value map that `ngMessages` listens on.