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December 17, 2014

Reusing Validation Messages in AngularJS

Filed under: AngularJS @ 1:03 pm
Tags: ,

One of the many new features in AngularJS 1.3 is the ability to reuse validation messages.

When displaying validation messages, you may find that you often reuse very similar messages:

“Class name must be entered.”  “Start date must be entered.”  “End date must be entered.”

Wouldn’t it be nice if you could reuse error messages instead of repeating them throughout the application? Angular 1.3 provides an ngMessagesInclude directive as part of the new Angular ngMessages module that allows you to share error messages throughout an application.

This post shows you how to use this new feature.

For more information about the new features in AngularJS 1.3, check out my latest Pluralsight course, authored with Joe Eames:

What’s New in Angular 1.3

screenshot

Reusing validation messages in Angular requires the following steps:

  1. Create an HTML file for the common messages.
  2. Include the HTML file in the same element as ngMessages.
  3. Override any messages as required.

Let’s take it one step at a time.

NOTE: If you are new to using ngMessages, check out the Angular 1.3 course.

Create the Messages File

The first step is to create the HTML template file for the common message text. In this file, add HTML with an ng-message attribute for each message. The value of the ng-message attribute must be a valid $error object key. That key is often the name of the validation type, for example: required, minlength, or maxlength.

The message text itself should be generic, meaning it should not refer to specific field names or field requirements.

The resulting HTML file could look something like this:

<span ng-message=”required”>
This item cannot be blank.</span>
<span ng-message=”minlength”>
You have not met this item’s minimum length.</span>
<span ng-message=”maxlength”>
You have exceeded this item’s maximum length.</span>

Include the HTML File

The next step is to include the messages HTML file for each input element that wants to reuse the messages using ng-messages-include. Insert this directive in the same element containing the ng-messages directive.

The following shows an Email field with a label, textbox, and validation. The entire form-group is shown below to provide context for the validation messages.

<div class=”form-group”
     ng-class=”{‘has-error’:classForm.inputInstructorEmail.$invalid &&
                            classForm.inputInstructorEmail.$touched}”>
    <label class=”col-md-2 control-label”
           for=”inputInstructorEmail”>Instructor’s Email</label>

    <div class=”col-md-4″>
        <input class=”form-control”
               type=”email”
               id=”inputInstructorEmail”
               name=”inputInstructorEmail”
               placeholder=”instructor’s email”
               ng-model=”vm.class.instructorEmail”
               required
               minlength=”6″ />
    </div>
    <span class=”help-block has-error”
          ng-if=”classForm.inputInstructorEmail.$touched”
          ng-messages=”classForm.inputInstructorEmail.$error”
          ng-messages-include=”app/errorMessages.html” >
        <span ng-message=”email”>
            Instructor’s email must be a valid email address.
        </span>
    </span>
</div>

Notice that the only ng-message directive included in the code above is for an invalid email address. This one is required here because it was not included in the messages html file.

Override Messages as Required

There may be times when you want a customized message. In those cases, you can easily override a message by simply adding a child element with an ng-message directive. The child element ng-message will always override any message defined for the same key in the included messages file.

    <span class=”help-block has-error”
          ng-if=”classForm.inputInstructorEmail.$touched”
          ng-messages=”classForm.inputInstructorEmail.$error”
          ng-messages-include=”app/errorMessages.html” >
        <span ng-message=”email”>
            Instructor’s email must be a valid email address.
        </span>
        <span ng-message=”minlength”>
            Instructor’s email must be at least 6 characters in length.
        </span>

    </span>

Use this technique any time you want to reuse messages throughout your application.

Enjoy!

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