5. Forms

We’ve all used a form to log in, submit a help request, place an order, book a flight, schedule a meeting and perform countless other data entry tasks. Forms are the mainstay of business applications.

Any seasoned web developer can slap together an HTML form with all the right tags. It's more challenging to create a cohesive data entry experience that guides the user efficiently and effectively through the workflow behind the form.

That takes design skills that are, to be frank, well out of scope for this chapter.

It also takes framework support for two-way data binding, change tracking, validation, and error handling ... which we shall cover in this chapter on Angular forms.

We will build a simple form from scratch, one step at a time. Along the way we'll learn how to

• build an Angular form with a component and template

• two-way data bind with [(ngModel)] syntax for reading and writing values to input controls

• track the change state and validity of form controls using ngModel in combination with a form

• provide strong visual feedback using special CSS classes that track the state of the controls

• display validation errors to users and enable/disable form controls

• use template reference variables for sharing information among HTML elements

Run the live example.

Template-Driven Forms

Many of us will build forms by writing templates in the Angular template syntax with the form-specific directives and techniques described in this chapter.

We can build almost any form we need with an Angular template — login forms, contact forms ... pretty much any business forms. We can lay out the controls creatively, bind them to data, specify validation rules and display validation errors, conditionally enable or disable specific controls, trigger built-in visual feedback, and much more.

It will be pretty easy because Angular handles many of the repetitive, boiler plate tasks we'd otherwise wrestle with ourselves.

We'll discuss and learn to build the following template-driven form:

Here at the Hero Employment Agency we use this form to maintain personal information about the heroes in our stable. Every hero needs a job. It's our company mission to match the right hero with the right crisis!

Two of the three fields on this form are required. Required fields have a green bar on the left to make them easy to spot.

If we delete the hero name, the form displays a validation error in an attention grabbing style:

Note that the submit button is disabled and the "required" bar to the left of the input control changed from green to red.

We will build this form in the following sequence of small steps

1. Create the Hero model class
2. Create the component that controls the form
3. Create a template with the initial form layout
4. Bind data properties to each form input control with the ngModel two-way data binding syntax
5. Add the name attribute to each form input control
6. Add custom CSS to provide visual feedback
7. Show and hide validation error messages
8. Handle form submission with ngSubmit
9. Disable the form’s submit button until the form is valid

Setup

Create a new project folder (angular2-forms) and follow the steps in the QuickStart.

Create the Hero Model Class

As users enter form data, we capture their changes and update an instance of a model. We can't layout the form until we know what the model looks like.

A model can be as simple as a "property bag" that holds facts about a thing of application importance. That describes well our Hero class with its three required fields (id, name, power) and one optional field (alterEgo).

Create a new file in the app folder called hero.ts and give it the following class definition:

export class Hero {

  constructor(
    public id: number,
    public name: string,
    public power: string,
    public alterEgo?: string
  ) {  }

}

It's an anemic model with few requirements and no behavior. Perfect for our demo.

The TypeScript compiler generates a public field for each public constructor parameter and assigns the parameter’s value to that field automatically when we create new heroes.

The alterEgo is optional and the constructor lets us omit it; note the (?) in alterEgo?.

We can create a new hero like this:

let myHero =  new Hero(42, 'SkyDog',
                       'Fetch any object at any distance',
                       'Leslie Rollover');
console.log('My hero is called ' + myHero.name); // "My hero is called SkyDog"

Create a Form component

An Angular form has two parts: an HTML-based template and a code-based Component to handle data and user interactions.

We begin with the Component because it states, in brief, what the Hero editor can do.

Create a new file called hero-form.component.ts and give it the following definition:

import { Component } from '@angular/core';

import { Hero }    from './hero';

@Component({
  selector: 'hero-form',
  templateUrl: 'app/hero-form.component.html'
})
export class HeroFormComponent {

  powers = ['Really Smart', 'Super Flexible',
            'Super Hot', 'Weather Changer'];

  model = new Hero(18, 'Dr IQ', this.powers[0], 'Chuck Overstreet');

  submitted = false;

  onSubmit() { this.submitted = true; }

  // TODO: Remove this when we're done
  get diagnostic() { return JSON.stringify(this.model); }
}

There’s nothing special about this component, nothing form-specific, nothing to distinguish it from any component we've written before.

Understanding this component requires only the Angular concepts we’ve learned in previous chapters

1. We import the Component decorator from the Angular library as we usually do.

2. We import the Hero model we just created.

3. The @Component selector value of "hero-form" means we can drop this form in a parent template with a <hero-form> tag.

4. The templateUrl property points to a separate file for the template HTML called hero-form.component.html.

5. We defined dummy data for model and powers as befits a demo. Down the road, we can inject a data service to get and save real data or perhaps expose these properties as inputs and outputs for binding to a parent component. None of this concerns us now and these future changes won't affect our form.

6. We threw in a diagnostic property at the end to return a JSON representation of our model. It'll help us see what we're doing during our development; we've left ourselves a cleanup note to discard it later.

Why don't we write the template inline in the component file as we often do elsewhere in the Developer Guide?

There is no “right” answer for all occasions. We like inline templates when they are short. Most form templates won't be short. TypeScript and JavaScript files generally aren't the best place to write (or read) large stretches of HTML and few editors are much help with files that have a mix of HTML and code. We also like short files with a clear and obvious purpose like this one.

We made a good choice to put the HTML template elsewhere. We'll write that template in a moment. Before we do, we'll take a step back and revise the app.module.ts and app.component.ts to make use of our new HeroFormComponent.

Revise the app.module.ts

app.module.ts defines the application's root module. In it we identify the external modules we'll use in our application and declare the components that belong to this module, such as our HeroFormComponent.

Because template-driven forms are in their own module, we need to add the FormsModule to the array of imports for our application module before we can use forms.

Replace the contents of the "QuickStart" version with the following:

import { NgModule }      from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { FormsModule }   from '@angular/forms';

import { AppComponent }  from './app.component';
import { HeroFormComponent } from './hero-form.component';

@NgModule({
  imports: [
    BrowserModule,
    FormsModule
  ],
  declarations: [
    AppComponent,
    HeroFormComponent
  ],
  bootstrap: [ AppComponent ]
})
export class AppModule { }

Revise the app.component.ts

app.component.ts is the application's root component. It will host our new HeroFormComponent.

Replace the contents of the "QuickStart" version with the following:

import { Component } from '@angular/core';

@Component({
  selector: 'my-app',
  template: '<hero-form></hero-form>'
})
export class AppComponent { }

Create an initial HTML Form Template

Create a new template file called hero-form.component.html and give it the following definition:

<div class="container">
    <h1>Hero Form</h1>
    <form>
      <div class="form-group">
        <label for="name">Name</label>
        <input type="text" class="form-control" id="name" required>
      </div>

      <div class="form-group">
        <label for="alterEgo">Alter Ego</label>
        <input type="text" class="form-control" id="alterEgo">
      </div>

      <button type="submit" class="btn btn-default">Submit</button>

    </form>
</div>

That is plain old HTML 5. We're presenting two of the Hero fields, name and alterEgo, and opening them up for user input in input boxes.

The Name <input> control has the HTML5 required attribute; the Alter Ego <input> control does not because alterEgo is optional.

We've got a Submit button at the bottom with some classes on it for styling.

We are not using Angular yet. There are no bindings. No extra directives. Just layout.

The container, form-group, form-control, and btn classes come from Twitter Bootstrap. Purely cosmetic. We're using Bootstrap to gussy up our form. Hey, what's a form without a little style!

Let's add the stylesheet.

1. Open a terminal window in the application root folder and enter the command:

   npm install bootstrap --save

2. Open index.html and add the following link to the <head>.

   <link rel="stylesheet" 
         href="node_modules/bootstrap/dist/css/bootstrap.min.css">
   

Add Powers with *ngFor

Our hero may choose one super power from a fixed list of Agency-approved powers. We maintain that list internally (in HeroFormComponent).

We'll add a select to our form and bind the options to the powers list using ngFor, a technique we might have seen before in the Displaying Data chapter.

Add the following HTML immediately below the Alter Ego group.

<div class="form-group">
  <label for="power">Hero Power</label>
  <select class="form-control" id="power" required>
    <option *ngFor="let p of powers" [value]="p">{{p}}</option>
  </select>
</div>

We are repeating the <options> tag for each power in the list of Powers. The p template input variable is a different power in each iteration; we display its name using the interpolation syntax with the double-curly-braces.

Two-way data binding with ngModel

Running the app right now would be disappointing.

We don't see hero data because we are not binding to the Hero yet. We know how to do that from earlier chapters. Displaying Data taught us Property Binding. User Input showed us how to listen for DOM events with an Event Binding and how to update a component property with the displayed value.

Now we need to display, listen, and extract at the same time.

We could use those techniques again in our form. Instead we'll introduce something new, the [(ngModel)] syntax, that makes binding our form to the model super-easy.

Find the <input> tag for the "Name" and update it like this

<input type="text"  class="form-control" id="name"
       required
       [(ngModel)]="model.name" name="name">
  TODO: remove this: {{model.name}}

Focus on the binding syntax: [(ngModel)]="...".

If we ran the app right now and started typing in the Name input box, adding and deleting characters, we'd see them appearing and disappearing from the interpolated text. At some point it might look like this.

The diagnostic is evidence that we really are flowing values from the input box to the model and back again. That's two-way data binding!

Notice that we also added a name attribute to our <input> tag and set it to "name" which makes sense for the hero's name. Any unique value will do, but using a descriptive name is helpful. Defining a name attribute is a requirement when using [(ngModel)] in combination with a form.

Let's add similar [(ngModel)] bindings and name attributes to Alter Ego and Hero Power. We'll ditch the input box binding message and add a new binding at the top to the component's diagnostic property. Then we can confirm that two-way data binding works for the entire Hero model.

After revision the core of our form should have three [(ngModel)] bindings and name attributes that look much like this:

{{diagnostic}}
<div class="form-group">
  <label for="name">Name</label>
  <input type="text" class="form-control" id="name"
         required
         [(ngModel)]="model.name" name="name">
</div>

<div class="form-group">
  <label for="alterEgo">Alter Ego</label>
  <input type="text"  class="form-control" id="alterEgo"
         [(ngModel)]="model.alterEgo" name="alterEgo">
</div>

<div class="form-group">
  <label for="power">Hero Power</label>
  <select class="form-control"  id="power"
          required
          [(ngModel)]="model.power" name="power">
    <option *ngFor="let p of powers" [value]="p">{{p}}</option>
  </select>
</div>

If we ran the app right now and changed every Hero model property, the form might display like this:

The diagnostic near the top of the form confirms that all of our changes are reflected in the model.

Delete the {{diagnostic}} binding at the top as it has served its purpose.

<input type="text" class="form-control" id="name"
       required
       [ngModel]="model.name" name="name"
       (ngModelChange)="model.name = $event" >
  TODO: remove this: {{model.name}}

Track change-state and validity with ngModel

A form isn't just about data binding. We'd also like to know the state of the controls on our form.

Using ngModel in a form gives us more than just two way data binding. It also tells us if the user touched the control, if the value changed, or if the value became invalid.

The NgModel directive doesn't just track state; it updates the control with special Angular CSS classes that reflect the state. We can leverage those class names to change the appearance of the control and make messages appear or disappear.

Let's add a temporary template reference variable named spy to the "Name" <input> tag and use the spy to display those classes.

<input type="text" class="form-control" id="name"
  required
  [(ngModel)]="model.name" name="name"
  #spy >
<br>TODO: remove this: {{spy.className}}

Now run the app and focus on the Name input box. Follow the next four steps precisely

1. Look but don't touch
2. Click in the input box, then click outside the text input box
3. Add slashes to the end of the name
4. Erase the name

The actions and effects are as follows:

We should be able to see the following four sets of class names and their transitions:

The (ng-valid | ng-invalid) pair are most interesting to us. We want to send a strong visual signal when the data are invalid and we want to mark required fields. So we add custom CSS for visual feedback.

Delete the #spy template reference variable and TODO as they have served their purpose.

Add Custom CSS for Visual Feedback

We realize we can mark required fields and invalid data at the same time with a colored bar on the left of the input box:

We achieve this effect by adding two styles to a new forms.css file that we add to our project as a sibling to index.html.

.ng-valid[required], .ng-valid.required  {
  border-left: 5px solid #42A948; /* green */
}

.ng-invalid:not(form)  {
  border-left: 5px solid #a94442; /* red */
}

These styles select for the two Angular validity classes and the HTML 5 "required" attribute.

We update the <head> of the index.html to include this style sheet.

<link rel="stylesheet" href="styles.css">
<link rel="stylesheet" href="forms.css">

Show and Hide Validation Error messages

We can do better.

The "Name" input box is required. Clearing it turns the bar red. That says something is wrong but we don't know what is wrong or what to do about it. We can leverage the ng-invalid class to reveal a helpful message.

Here's the way it should look when the user deletes the name:

To achieve this effect we extend the <input> tag with

1. a template reference variable
2. the "is required" message in a nearby <div> which we'll display only if the control is invalid.

Here's how we do it for the name input box:

        <label for="name">Name</label>
        <input type="text" class="form-control" id="name"
               required
               [(ngModel)]="model.name" name="name"
               #name="ngModel" >
        <div [hidden]="name.valid || name.pristine" 
             class="alert alert-danger">
          Name is required
        </div>

We need a template reference variable to access the input box's Angular control from within the template. Here we created a variable called name and gave it the value "ngModel".

<div [hidden]="name.valid || name.pristine" 
     class="alert alert-danger">

In this example, we hide the message when the control is valid or pristine; pristine means the user hasn't changed the value since it was displayed in this form.

This user experience is the developer's choice. Some folks want to see the message at all times. If we ignore the pristine state, we would hide the message only when the value is valid. If we arrive in this component with a new (blank) hero or an invalid hero, we'll see the error message immediately, before we've done anything.

Some folks find that behavior disconcerting. They only want to see the message when the user makes an invalid change. Hiding the message while the control is "pristine" achieves that goal. We'll see the significance of this choice when we add a new hero to the form.

The Hero Alter Ego is optional so we can leave that be.

Hero Power selection is required. We can add the same kind of error handling to the <select> if we want but it's not imperative because the selection box already constrains the power to valid value.

Add a hero and reset the form

We'd like to add a new hero in this form. We place a "New Hero" button at the bottom of the form and bind its click event to a component method.

<button type="button" class="btn btn-default" (click)="newHero()">New Hero</button>

newHero() {
  this.model = new Hero(42, '', '');
}

Run the application again, click the New Hero button, and the form clears. The required bars to the left of the input box are red, indicating invalid name and power properties. That's understandable as these are required fields. The error messages are hidden because the form is pristine; we haven't changed anything yet.

Enter a name and click New Hero again. This time we see an error message! Why? We don't want that when we display a new (empty) hero.

Inspecting the element in the browser tools reveals that the name input box is no longer pristine. Replacing the hero did not restore the pristine state of the control.

We'll have to reset the form controls manually with a small trick. We add an active flag to the component, initialized to true. When we add a new hero, we toggle active false and then immediately back to true with a quick setTimeout.

  active = true;

  newHero() {
    this.model = new Hero(42, '', '');
    this.active = false;
    setTimeout(() => this.active = true, 0);
  }

Then we bind the form element to this active flag.

<form *ngIf="active">

With NgIf bound to the active flag, clicking "New Hero" removes the form from the DOM and recreates it in a blink of an eye. The re-created form is in a pristine state. The error message is hidden.

Submit the form with ngSubmit

The user should be able to submit this form after filling it in. The Submit button at the bottom of the form does nothing on its own but it will trigger a form submit because of its type (type="submit").

A "form submit" is useless at the moment. To make it useful, we'll update the <form> tag with another Angular directive, NgSubmit, and bind it to the HeroFormComponent.submit() method with an event binding

<form *ngIf="active" (ngSubmit)="onSubmit()" #heroForm="ngForm">

We slipped in something extra there at the end! We defined a template reference variable, #heroForm, and initialized it with the value, "ngForm".

The variable heroForm is now a reference to the NgForm directive that governs the form as a whole.

Later in the template we bind the button's disabled property to the form's over-all validity via the heroForm variable. Here's that bit of markup:

<button type="submit" class="btn btn-default" [disabled]="!heroForm.form.valid">Submit</button>

Re-run the application. The form opens in a valid state and the button is enabled.

Now delete the Name. We violate the "name required" rule which is duly noted in our error message as before. And now the Submit button is also disabled.

Not impressed? Think about it for a moment. What would we have to do to wire the button's enable/disabled state to the form's validity without Angular's help?

For us, it was as simple as

1. Define a template reference variable on the (enhanced) form element
2. Reference that variable in a button some 50 lines away.

Toggle two form regions (extra credit)

Submitting the form isn't terribly dramatic at the moment.

Let's do something more strikingly visual. Let's hide the data entry area and display something else.

Start by wrapping the form in a <div> and bind its hidden property to the HeroFormComponent.submitted property.

  <div  [hidden]="submitted">
    <h1>Hero Form</h1>
    <form *ngIf="active" (ngSubmit)="onSubmit()" #heroForm="ngForm">

       <!-- ... all of the form ... -->

    </form>
  </div>

The main form is visible from the start because the the submitted property is false until we submit the form, as this fragment from the HeroFormComponent reminds us:

submitted = false;

onSubmit() { this.submitted = true; }

When we click the Submit button, the submitted flag becomes true and the form disappears as planned.

Now we need to show something else while the form is in the submitted state. Add the following block of HTML below the <div> wrapper we just wrote:

<div [hidden]="!submitted">
  <h2>You submitted the following:</h2>
  <div class="row">
    <div class="col-xs-3">Name</div>
    <div class="col-xs-9  pull-left">{{ model.name }}</div>
  </div>
  <div class="row">
    <div class="col-xs-3">Alter Ego</div>
    <div class="col-xs-9 pull-left">{{ model.alterEgo }}</div>
  </div>
  <div class="row">
    <div class="col-xs-3">Power</div>
    <div class="col-xs-9 pull-left">{{ model.power }}</div>
  </div>
  <br>
  <button class="btn btn-default" (click)="submitted=false">Edit</button>
</div>

There's our hero again, displayed read-only with interpolation bindings. This slug of HTML only appears while the component is in the submitted state.

We added an Edit button whose click event is bound to an expression that clears the submitted flag.

When we click it, this block disappears and the editable form reappears.

That's as much drama as we can muster for now.

Conclusion

The Angular form techniques discussed in this chapter take advantage of the following framework features to provide support for data modification, validation and more:

• An Angular HTML form template.
• A form component class with a Component decorator.
• The ngSubmit directive for handling the form submission.
• Template reference variables such as #heroForm, #name and #power.
• The [(ngModel)] syntax and a name attribute for two-way data binding, validation and change tracking.
• The reference variable’s valid property on input controls to check if a control is valid and show/hide error messages.
• Controlling the submit button's enabled state by binding to NgForm validity.
• Custom CSS classes that provide visual feedback to users about invalid controls.

Our final project folder structure should look like this:

Here’s the final version of the source:

import { Component } from '@angular/core';

import { Hero }    from './hero';

@Component({
  selector: 'hero-form',
  templateUrl: 'app/hero-form.component.html'
})
export class HeroFormComponent {

  powers = ['Really Smart', 'Super Flexible',
            'Super Hot', 'Weather Changer'];

  model = new Hero(18, 'Dr IQ', this.powers[0], 'Chuck Overstreet');

  submitted = false;

  onSubmit() { this.submitted = true; }

  // Reset the form with a new hero AND restore 'pristine' class state
  // by toggling 'active' flag which causes the form
  // to be removed/re-added in a tick via NgIf
  // TODO: Workaround until NgForm has a reset method (#6822)
  active = true;

  newHero() {
    this.model = new Hero(42, '', '');
    this.active = false;
    setTimeout(() => this.active = true, 0);
  }
}

<div class="container">
  <div  [hidden]="submitted">
    <h1>Hero Form</h1>
    <form *ngIf="active" (ngSubmit)="onSubmit()" #heroForm="ngForm">
      <div class="form-group">
        <label for="name">Name</label>
        <input type="text" class="form-control" id="name"
               required
               [(ngModel)]="model.name" name="name"
               #name="ngModel" >
        <div [hidden]="name.valid || name.pristine" 
             class="alert alert-danger">
          Name is required
        </div>
      </div>

      <div class="form-group">
        <label for="alterEgo">Alter Ego</label>
        <input type="text" class="form-control" id="alterEgo"
               [(ngModel)]="model.alterEgo" name="alterEgo" >
      </div>

      <div class="form-group">
        <label for="power">Hero Power</label>
        <select class="form-control" id="power"
                required
                [(ngModel)]="model.power" name="power" 
                #power="ngModel" >
          <option *ngFor="let p of powers" [value]="p">{{p}}</option>
        </select>
        <div [hidden]="power.valid || power.pristine" class="alert alert-danger">
          Power is required
        </div>
      </div>

      <button type="submit" class="btn btn-default" [disabled]="!heroForm.form.valid">Submit</button>

      <button type="button" class="btn btn-default" (click)="newHero()">New Hero</button>

    </form>
  </div>

  <div [hidden]="!submitted">
    <h2>You submitted the following:</h2>
    <div class="row">
      <div class="col-xs-3">Name</div>
      <div class="col-xs-9  pull-left">{{ model.name }}</div>
    </div>
    <div class="row">
      <div class="col-xs-3">Alter Ego</div>
      <div class="col-xs-9 pull-left">{{ model.alterEgo }}</div>
    </div>
    <div class="row">
      <div class="col-xs-3">Power</div>
      <div class="col-xs-9 pull-left">{{ model.power }}</div>
    </div>
    <br>
    <button class="btn btn-default" (click)="submitted=false">Edit</button>
  </div>
</div>

export class Hero {

  constructor(
    public id: number,
    public name: string,
    public power: string,
    public alterEgo?: string
  ) {  }

}

import { NgModule }      from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { FormsModule }   from '@angular/forms';

import { AppComponent }  from './app.component';
import { HeroFormComponent } from './hero-form.component';

@NgModule({
  imports: [
    BrowserModule,
    FormsModule
  ],
  declarations: [
    AppComponent,
    HeroFormComponent
  ],
  bootstrap: [ AppComponent ]
})
export class AppModule { }

import { Component } from '@angular/core';

@Component({
  selector: 'my-app',
  template: '<hero-form></hero-form>'
})
export class AppComponent { }

import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';
import { AppModule } from './app.module';

// Compiles the module (asynchronously) with the runtime compiler
// which generates a compiled module factory in memory.
// Then bootstraps with that factory, targeting the browser.
platformBrowserDynamic().bootstrapModule(AppModule);

<html>
  <head>
    <title>Hero Form</title>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">

    <link rel="stylesheet" 
          href="node_modules/bootstrap/dist/css/bootstrap.min.css">
    <link rel="stylesheet" href="styles.css">
    <link rel="stylesheet" href="forms.css">

    <!-- Polyfill(s) for older browsers -->
    <script src="node_modules/core-js/client/shim.min.js"></script>

    <script src="node_modules/zone.js/dist/zone.js"></script>
    <script src="node_modules/reflect-metadata/Reflect.js"></script>
    <script src="node_modules/systemjs/dist/system.src.js"></script>

    <script src="systemjs.config.js"></script>
    <script>
      System.import('app').catch(function(err){ console.error(err); });
    </script>
  </head>

  <body>
    <my-app>Loading...</my-app>
  </body>

</html>

.ng-valid[required], .ng-valid.required  {
  border-left: 5px solid #42A948; /* green */
}

.ng-invalid:not(form)  {
  border-left: 5px solid #a94442; /* red */
}