include ../_util-fns :marked We’ve all used a form to login, 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 - The `ngModel` two-way data binding syntax for reading and writing values to input controls - The `ngControl` directive to track the change state and validity of form controls - The special CSS classes that `ngControl` adds to form controls and how we can use them to provide strong visual feedback - How to display validation errors to users and enable/disable form controls - How to share information across controls with template local variables [Live Example](/resources/live-examples/forms/js/plnkr.html) .l-main-section :marked ## Template-Driven Forms Many of us will build forms by writing templates in the Angular [template syntax](./template-syntax.html) with the form-specific directives and techniques described in this chapter. .l-sub-section :marked That's not the only way to create a form but it's the way we'll cover in this chapter. :marked 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: figure.image-display img(src="/resources/images/devguide/forms/hero-form-1.png" width="400px" alt="Clean Form") :marked 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: figure.image-display img(src="/resources/images/devguide/forms/hero-form-2.png" width="400px" alt="Invalid, Name Required") :marked Note that the submit button is disabled and the "required" bar to the left of the input control changed from green to red. .l-sub-section p We'll' customize the colors and location of the "required" bar with standard CSS. :marked We will build this form in the following sequence of small steps 1. Create the `Hero` model class 1. Create the component that controls the form 1. Create a template with the initial form layout 1. Add the **ngModel** directive to each form input control 1. Add the **ngControl** directive to each form input control 1. Add custom CSS to provide visual feedback 1. Show and hide validation error messages 1. Handle form submission with **ngSubmit** 1. Disable the form’s submit button until the form is valid :marked ## Setup Create a new project folder (`angular2-forms`) and follow the steps in the [QuickStart](../quickstart.html). ## 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.js` and give it the following constructor: +makeExample('forms/js/app/hero.js', null, 'app/hero.js') :marked It's an anemic model with few requirements and no behavior. Perfect for our demo. The `alterEgo` is optional and the constructor lets us omit it by being the last argument. We can create a new hero like this: code-example(format=""). var 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" :marked We update the `` of the `index.html` to include this javascript file. +makeExample('forms/js/index.html', 'scripts-hero', 'index.html (excerpt)')(format=".") .l-main-section :marked ## 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.js` and give it the following definition: +makeExample('forms/js/app/hero-form.component.js', 'first', 'app/hero-form.component.js') :marked 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 2 concepts we’ve learned in previous chapters 1. We use the `ng.core` object from the Angular library as we usually do. 1. The `Component()` selector value of "hero-form" means we can drop this form in a parent template with a `` tag. 1. The `templateUrl` property points to a separate file for template HTML called `hero-form.component.html`. 1. 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](./template-syntax.html#inputs-outputs) for binding to a parent component. None of this concerns us now and these future changes won't affect our form. 1. We threw in a `diagnostic` method 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.component.js` to make use of our new `HeroFormComponent`. :marked Again we update the `` of the `index.html` to include the new javascript file. +makeExample('forms/js/index.html', 'scripts-hero-form', 'index.html (excerpt)')(format=".") .l-main-section :marked ## Revise the *app.component.js* `app.component.js` is the application's root component. It will host our new `HeroFormComponent`. Replace the contents of the "QuickStart" version with the following: +makeExample('forms/js/app/app.component.js', null, 'app/app.component.js') :marked .l-sub-section :marked There are only two changes: 1. The `template` is simply the new element tag identified by the component's `select` property. 1. The `directives` array tells Angular that our template depends upon the `HeroFormComponent` which is itself a Directive (as are all Components). .l-main-section :marked ## Create an initial HTML Form Template Create a new template file called `hero-form.component.html` and give it the following definition: +makeExample('forms/js/app/hero-form.component.html', 'start', 'app/hero-form.component.html') :marked 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* `` control has the HTML5 `required` attribute; the *Alter Ego* `` control does not because `alterEgo` is optional. We've got a *Submit* button at the bottom with some classes on it. **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 Boostrap](http://getbootstrap.com/css/). Purely cosmetic. We're using Bootstrap to gussy up our form. Hey, what's a form without a little style! .callout.is-important header Angular Forms Do Not Require A Style Library :marked Angular makes no use of the `container`, `form-group`, `form-control`, and `btn` classes or the styles of any external library. Angular apps can use any CSS library ... or none at all. :marked Let's add the stylesheet. ol li Open a terminal window in the application root folder and enter the command: code-example(language="html" escape="html"). npm install bootstrap --save li Open index.html and add the following link to the <head>. +makeExample('forms/js/index.html', 'bootstrap')(format=".") :marked .l-main-section :marked ## 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](./displaying-data.html) chapter. Add the following HTML *immediately below* the *Alter Ego* group. +makeExample('forms/js/app/hero-form.component.html', 'powers', 'app/hero-form.component.html (excerpt)')(format=".") :marked We are repeating the `` tag for each power in the list of Powers. The `#p` local template variable is a different power in each iteration; we display its name using the interpolation syntax with the double-curly-braces. .l-main-section :marked ## Two-way data binding with ***ngModel** Running the app right now would be disappointing. figure.image-display img(src="/resources/images/devguide/forms/hero-form-3.png" width="400px" alt="Early form with no binding") :marked 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](./displaying-data.html) taught us Property Binding. [User Input](./user-input.html) 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` directive, that makes binding our form to the model super-easy. Find the `` tag for the "Name" and update it like this +makeExample('forms/js/app/hero-form.component.html', 'ngModel-1','app/hero-form.component.html (excerpt)')(format=".") .l-sub-section :marked We appended a diagnostic interpolation after the input tag so we can see what we're doing. We left ourselves a note to throw it way when we're done. :marked 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. figure.image-display img(src="/resources/images/devguide/forms/ng-model-in-action.png" width="400px" alt="ngModel in action") :marked 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!** Let's add similar `[(ngModel)]` bindings 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` method. 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 that look much like this: +makeExample('forms/js/app/hero-form.component.html', 'ngModel-2', 'app/hero-form.component.html (excerpt)') :marked If we ran the app right now and changed every Hero model property, the form might display like this: figure.image-display img(src="/resources/images/devguide/forms/ng-model-in-action-2.png" width="400px" alt="ngModel in super action") :marked 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. .l-sub-section :marked ### Inside [(ngModel)] *This section is an optional deep dive into [(ngModel)]. Not interested? Skip ahead!* The punctuation in the binding syntax, [()], is a good clue to what's going on. In a Property Binding, a value flows from the model to a target property on screen. We identify that target property by surrounding its name in brackets, []. This is a one-way data binding **from the model to the view**. In an Event Binding, we flow the value from the target property on screen to the model. We identify that target property by surrounding its name in parentheses, (). This is a one-way data binding in the opposite direction **from the view to the model**. No wonder Angular chose to combine the punctuation as [()] to signify a two-way data binding and a **flow of data in both directions**. In fact, we can break the `NgModel` binding into its two separate modes as we do in this re-write of the "Name" `` binding: +makeExample('forms/js/app/hero-form.component.html', 'ngModel-3','app/hero-form.component.html (excerpt)')(format=".") :marked
The Property Binding should feel familiar. The Event Binding might seem strange. The `ngModelChange` is not an `` element event. It is actually an event property of the `NgModel` directive. When Angular sees a binding target in the form [(x)], it expects the `x` directive to have an `x` input property and an `xChange` output property. The other oddity is the template expression, `model.name = $event`. We're used to seeing an `$event` object coming from a DOM event. The `ngModelChange` property doesn't produce a DOM event; it's an Angular `EventEmitter` property that returns the input box value when it fires — which is precisely what we should assign to the model's `name' property. Nice to know but is it practical? We almost always prefer `[(ngModel)]`. We might split the binding if we had to do something special in the event handling such as debounce or throttle the key strokes. Learn more about `NgModel` and other template syntax in the [Template Syntax](./template-syntax.html) chapter. .l-main-section :marked ## Track change-state and validity with **ngControl** A form isn't just about data binding. We'd also like to know the state of the controls on our form. The `NgControl` directive keeps track of control state for us. .callout.is-helpful header NgControl requires Form :marked The `NgControl` is one of a family of `NgForm` directives that can only be applied to a control within a ` tag. :marked Our application can ask an `NgControl` if the user touched the control, if the value changed, or if the value became invalid. `NgControl` doesn't just track state; it updates the control with special Angular CSS classes from the set we listed above. We can leverage those class names to change the appearance of the control and make messages appear or disappear. We'll explore those effects soon. Right now we should **add `ngControl`to all three form controls**, starting with the *Name* input box +makeExample('forms/js/app/hero-form.component.html', 'ngControl-1', 'app/hero-form.component.html (excerpt)')(format=".") :marked Be sure to assign a unique name to each `ngControl` directive. .l-sub-section :marked Angular registers controls under their `ngControl` names with the `NgForm`. We didn't add the `NgForm` directive explicitly but it's here and we'll talk about it [later in this chapter](#ngForm). .l-main-section :marked ## Add Custom CSS for Visual Feedback `NgControl` doesn't just track state. It updates the control with three classes that reflect the state. table tr th State th Class if true th Class if false tr td Control has been visited td ng-touched td ng-untouched tr td Control's value has changed td ng-dirty td ng-pristine tr td Control's value is valid td ng-valid td ng-invalid :marked Let's add a temporary [local template variable](./template-syntax.html#local-vars) named **spy** to the "Name" `` tag and use the spy to display those classes. +makeExample('forms/js/app/hero-form.component.html', 'ngControl-2','app/hero-form.component.html (excerpt)')(format=".") :marked Now run the app and focus on the *Name* input box. Follow the next four steps *precisely* 1. Look but don't touched 1. Click in the input box, then click outside the text input box 1. Add slashes to the end of the name 1. Erase the name The actions and effects are as follows: figure.image-display img(src="/resources/images/devguide/forms/control-state-transitions-anim.gif" alt="Control State Transition") :marked We should be able to see the following four sets of class names and their transitions: figure.image-display img(src="/resources/images/devguide/forms/ng-control-class-changes.png" width="400px" alt="Control State Transitions") :marked 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. We realize we can do both at the same time with a colored bar on the left of the input box: figure.image-display img(src="/resources/images/devguide/forms/validity-required-indicator.png" width="400px" alt="Invalid Form") :marked 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`. +makeExample('forms/js/forms.css',null,'forms.css')(format=".") :marked These styles select for the two Angular validity classes and the HTML 5 "required" attribute. We update the `` of the `index.html` to include this style sheet. +makeExample('forms/js/index.html', 'styles', 'index.html (excerpt)')(format=".") :marked ## 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: figure.image-display img(src="/resources/images/devguide/forms/name-required-error.png" width="400px" alt="Name required") :marked To achieve this effect we extend the `` tag with 1. a [local template variable](./template-syntax.html#local-vars) 1. the "*is required*" message in a nearby `
` which we'll display only if the control is invalid. Here's how we do it for the *name* input box: -var stylePattern = { otl: /(#name="form")|(.*div.*$)|(Name is required)/gm }; +makeExample('forms/js/app/hero-form.component.html', 'name-with-error-msg', 'app/hero-form.component.html (excerpt)', stylePattern) :marked When we added the `ngControl` directive, we bound it to the model's `name` property. Here we initialize a template local variable (`name`) with the value "ngForm" (`#name="ngForm"`). Angular recognizes that syntax and re-sets the `name` local template variable to the `ngControl` directive instance. In other words, the `name` local template variable becomes a handle on the `ngControl` object for this input box. Now we can control visibility of the "name" error message by binding the message `
` element's `hidden` property to the `ngControl` object's `valid` property. The message is hidden while the control is valid; the message is revealed when the control becomes invalid. .l-sub-section :marked ### The NgForm directive We just set a template local variable with the value of an `NgForm` directive. Why did that work? We didn't add the **[`NgForm`](../api/common/NgForm-directive.html) directive** explicitly. Angular added it surreptiously, wrapping it around the `
` element The `NgForm` directive supplements the `form` element with additional features. It collects `Controls` (elements identified by an `ngControl` directive) and monitors their properties including their validity. It also has its own `valid` property which is true only if every contained control is valid. :marked 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 `