Utility library to improve the robustness of your Angular forms.
Whether you have simple and tiny forms or huge and complex ones, ngx-sub-form
will help you build a solid base for them.
ControlValueAccessor
by hand, no inheritance, no boilerplate. Only one function to create all your forms!Please note one thing: If your goal is to generate forms dynamically (based on some JSON configuration for example) ngx-sub-form
is not here for that!
As a picture is often worth a 1000 words, let's take a quick overlook at the API before explaining in details further on:
ngx-sub-form
is available on NPM:
npm i ngx-sub-form
Note about the versions:
@angular version |
ngx-sub-form version |
---|---|
v <= 7 |
v <= 2.7.1 |
8.x |
4.x |
9.x <= v <= 12.x |
5.1.2 |
13.x |
5.2.0 (non breaking but new API available as well) |
14.x |
6.0.0 (Angular 14 upgrade only) |
14.x |
7.0.0 (deprecated API is now removed) |
15.x |
8.0.0 |
16.x |
9.0.0 |
17.x |
10.0.0 |
18.x |
11.0.0 |
There's one function available to create all your forms: createForm
.
This function takes as parameter a configuration object and returns an object ready to be used to use your form and all its new utilities. In this section we'll discover what configuration we can pass to createForm
and what exactly we'll be getting back.
createForm
configuration object:Key | Type | Optional or required | Root form | Sub form | What is it for? |
---|---|---|---|---|---|
formType |
FormType |
Required | ✅ | ✅ | Defines the type of the form. Can either be FormType.ROOT or FormType.SUB |
disabled$ |
Observable<boolean> |
Required | ✅ | ❌ | When this observable emits true , the whole form (including the root form and all the sub forms) will be disabled |
input$ |
Observable<ControlInterface \| undefined> |
Required | ✅ | ❌ | A root form is a component in between the parent passing raw data and the form itself. This property is an observable that you must provide which will be used behind the scenes to update for you the form values |
output$ |
Subject<ControlInterface> |
Required | ✅ | ❌ | A root form is a component in between the parent passing raw data and the form itself. This property is an observable that you must provide which will be used behind the scenes to broadcast the form value to the parent when it changes |
manualSave$ |
Observable<void> |
Optional | ✅ | ❌ | By default a root form will automatically broadcast all the form updates (through the output$ ) as soon as there's a change. If you wish to "save" the form only when you click on a save button for example, you can create a subject on your side and pass it here. Whenever you call next on your subject, assuming the form is valid, it'll broadcast te form value to the parent (through the output$ ) |
outputFilterPredicate |
(currentInputValue: FormInterface, outputValue: FormInterface) => boolean |
Optional | ✅ | ❌ | The default behaviour is to compare the current transformed value of input$ with the current value of the form (deep check), and if these are equal, the value won't be passed to output$ in order to prevent the broadcast |
handleEmissionRate |
(obs$: Observable<FormInterface>) => Observable<FormInterface> |
Optional | ✅ | ❌ | If you want to control how frequently the form emits on the output$ , you can customise the emission rate with this. Example: handleEmissionRate: formValue$ => formValue$.pipe(debounceTime(300)) |
As simple as forms can look when they only have a few fields, their complexity can increase quite quickly. In order to keep your code as simple as possible and isolate the different concepts, we do recommend to write forms in complete isolation from the rest of your app.
In order to do so, you can create some top level forms that we call "root forms". As one form can become bigger and bigger over time, we also help by letting you create "sub forms" (without the pain of dealing manually with a ControlValueAccessor!). Let's dig into their specifics, how they differ and how to use them.
Root forms let you isolate a form from the rest of your app.
You can encapsulate them and (pretty much) never have to deal with patchValue
or setValue
to update the form nor subscribe to valueChanges
to listen to the updates.
Instead, you'll be able to create a dedicated form component and pass data using an input, receive updates using an output. Just like you would with a dumb component.
Let's have a look with a very simple workflow:
In this scenario, the smart component could look like the following:
@Component({
selector: 'person-container',
template: `
<person-form [person]="person$ | async" (personUpdate)="personUpdate($event)"></person-form>
`,
})
export class PersonContainer {
public person$: Observable<Person> = this.personService.person$;
constructor(private personService: PersonService) {}
public personUpdate(person: Person): void {
this.personService.update(person);
}
}
This component is only responsible to get the correct data and manage updates (if any). It completely delegates to the root form:
Now let's talk about the actual root form:
@Component({
selector: 'person-form',
template: `
<form [formGroup]="form.formGroup">
<input type="text" [formControlName]="form.formControlNames.firstName" />
<input type="text" [formControlName]="form.formControlNames.lastName" />
<address-control [formControlName]="form.formControlNames.address"></address-control>
</form>
`,
})
export class PersonForm {
private input$: Subject<Person | undefined> = new Subject();
@Input() set person(person: Person | undefined) {
this.input$.next(person);
}
private disabled$: Subject<boolean> = new Subject();
@Input() set disabled(value: boolean | undefined) {
this.disabled$.next(!!value);
}
@Output() personUpdate: Subject<Person> = new Subject();
public form = createForm<Person>(this, {
formType: FormType.ROOT,
disabled$: this.disabled$,
input$: this.input$,
output$: this.personUpdate,
formControls: {
id: new FormControl(null, Validators.required),
firstName: new FormControl(null, Validators.required),
lastName: new FormControl(null, Validators.required),
address: new FormControl(null, Validators.required),
},
});
}
We'll go through the example above bit by bit.
public form = createForm<Person>(this, {
formType: FormType.ROOT,
disabled$: this.disabled$,
input$: this.input$,
output$: this.personUpdate,
formControls: {
id: new FormControl(null, Validators.required),
firstName: new FormControl(null, Validators.required),
lastName: new FormControl(null, Validators.required),
address: new FormControl(null, Validators.required),
},
});
This is what we provide to create a form with ngx-sub-form
:
FormType.ROOT
or FormType.SUB
)disabled$
stream to know whether we should disable the whole form or not (including all the sub forms as well)input$
stream which is the data we'll use to update the formoutput$
stream, which would usually be our EventEmitter
so that a parent component can listen to the form update through an outputformControls
, which is exactly what you'd pass when creating a FormGroup
One thing to note: The createForm
function takes a generic which will let you type our form. In this case, if you forgot to pass a property of the form in the formControls
it'd be caught at build time by Typescript.
private input$: Subject<Person | undefined> = new Subject();
@Input() set person(person: Person | undefined) {
this.input$.next(person);
}
private disabled$: Subject<boolean> = new Subject();
@Input() set disabled(value: boolean | undefined) {
this.disabled$.next(!!value);
}
This is simply a way of binding an input to an observable. We do this because the createForm
function requires us to pass an input$
stream and a disabled$
one. Hopefully Angular lets us one day access inputs as observables natively. In the meantime if you want to reduce this boilerplate even further, you can search on NPM for libraries which are doing this already. It's not as good as what Angular could do if it was built in, but it's still useful.
@Output() personUpdate: Subject<Person> = new Subject();
This is an Output
. It could be an EventEmitter
if you prefer a "classic" way of creating an output but really all we need is a Subject
so that internally, the createForm
function is able to push the form value whenever it's been updated.
Finally, our template:
<form [formGroup]="form.formGroup">
<input type="text" [formControlName]="form.formControlNames.firstName" />
<input type="text" [formControlName]="form.formControlNames.lastName" />
<address-control [formControlName]="form.formControlNames.address"></address-control>
</form>
Our createForm
function will return an object of type NgxRootForm
. It means we'll then have access to the following properties:
formGroup
: The FormGroup
instance with augmented capacity for type safety. While at runtime this object is really the form group itself, it is now defined as a TypedFormGroup<FormInterface>
which provides type safety on a bunch of attributes and methods (value
, valueChanges
, controls
, setValue
, patchValue
, getRawValue
). If you want to know more about the TypedFormGroup
interface, have a look in projects/ngx-sub-form/src/lib/shared/ngx-sub-form-utils.ts
formControlNames
: A typed object containing our form control names. The advantage of using this instead of a simple string is in case you ever update the type passed as the generic of the form (through a refactor or a change in the API upstream, etc). If you remove or update an existing property and forget to update the template, Typescript will catch the error (assuming you're using AoT which is the case by default)formGroupErrors
: An object holding all the errors in the form. Bonus point: It also includes all the nested errors from the sub forms!controlValue$
: If you want to listen to the form value, just use form.formGroup.valueChanges
. But keep in mind that it will not be triggered when the form is being updated by the parent ⚠️. It'll only be triggered when the form is changed locally. If you want to know what's the latest form value from either the parent OR the local changes, you should use form.controlValue$
insteadcreateFormArrayControl
: We'll cover this one in the remap section, after the sub formsWhen you've got a form represented by an object containing not one level of info but multiple ones (like a person which has an address, the address contains itself multiple fields), you should create a sub form to manage the address
in isolation.
This is great for a couple of reasons:
Here's a full example:
@Component({
selector: 'address-control',
template: `
<div [formGroup]="form.formGroup">
<input type="text" [formControlName]="form.formControlNames.street" />
<input type="text" [formControlName]="form.formControlNames.city" />
<input type="text" [formControlName]="form.formControlNames.state" />
<input type="number" [formControlName]="form.formControlNames.zipCode" />
</div>
`,
providers: subformComponentProviders(PersonForm),
})
export class PersonForm {
public form = createForm<Address>(this, {
formType: FormType.SUB,
formControls: {
street: new FormControl(null, Validators.required),
city: new FormControl(null, Validators.required),
state: new FormControl(null, Validators.required),
zipCode: new FormControl(null, Validators.required),
},
});
}
A sub form looks very much like a root form but with an API that is even simpler.
When you call the createForm
function, start by setting the formType
to FormType.SUB
and then define your formControls
.
One important thing to note:
providers: subformComponentProviders(PersonForm);
subformComponentProviders
is only here to help reduce the number of lines needed for each sub form component. It returns the following providers:
return [
{
provide: NG_VALUE_ACCESSOR,
useExisting: component,
multi: true,
},
{
provide: NG_VALIDATORS,
useExisting: component,
multi: true,
},
];
Behind the scenes those providers are allowing us to have a component considered as a ControlValueAccessor.
If you've ever created a ControlValueAccessor
yourself, you can probably appreciate the amount of boilerplate ngx-sub-form
is removing while adding features on top of it.
Just like the root form, the createForm
function will return an object containing the following:
formGroup
formControlNames
formGroupErrors
createFormArrayControl
controlValue$
As they're exactly the same as the ones in the root form we're not going to go over them again, feel free to check the previous section.
Sometimes a given data structure may not match the one you'd like to have internally for a form. When that's the case, ngx-sub-form
offers 2 functions to:
Here are the 2 interfaces:
toFormGroup: (obj: ControlInterface) => FormInterface;
fromFormGroup: (formValue: FormInterface) => ControlInterface;
Example of a remap could be getting a date object that you want to convert to an ISO string date before passing that value to a date picker and before broadcasting that value back to the parent, convert it back to a date. Or vice versa.
A really interesting use case is to deal with polymorphic values. If we take the example of our live demo: https://cloudnc.github.io/ngx-sub-form we've got src/app/main/listing/listing-form/listing-form.component.ts
. This form can receive either a vehicle
or a droid
. While polymorphism works great on typescript side, when it comes to templates... It's an other story! The best way is to have 2 sub components, which will handle 1 and 1 thing: Either a vehicle
or a droid
. And in the template use an ngIf
or an ngSwitch
to dynamically create the expected sub form.
That said, to be able to switch
on a value, we need to know that value: A discriminator. It'll let us know what's the type of our current object really easily, without having to create a type guard for example. And a remap is a perfect candidate for this. If you want a full example please have a look to the listing-form.component.ts
(path shown above).
When your data structure contains one or more arrays, you may want to simply display the values in the view but chances are you want to bind them to the form.
In that case, working with a FormArray
is the right way to go and for that, we will take advantage of the remap principles explained in the previous section.
If you have custom validations to set on the form controls, you can implement the createFormArrayControl
function, which gives the library a hook with which to construct new form controls for the form array with the correct validators applied.
Its definition is the following:
createFormArrayControl(key, value) => FormControl;
Where key is a key of your main form and value, its associated value.
To see a complete example please refer to src/app/main/listing/listing-form/vehicle-listing/crew-members/crew-members.component.ts
and its html
part.
Please, feel free to contribute to ngx-sub-form
.
We've done our best to come up with a solution that helped us and our own needs when dealing with forms. But we might have forgotten some use cases that might be worth implementing in the core or the lib rather than on every project.
Remember that contributing doesn't necessarily mean to make a pull request, you can raise an issue, edit the documentation (readme), etc.
We'd love to know more about who's using ngx-sub-form in production and on what kind of project! We've created an issue where everyone can share more about their experience.