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Angular JavaScript

Introduction to Angular Reactive Forms

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Angular is a popular front-end framework made by Google. Like other popular front-end frameworks, it uses a component-based architecture to structure apps.

In this article, we’ll look at the basics of creating reactive forms with Angular.

Reactive Forms

Reactive forms use an explicit and immutable approach to managing the state of a form at a given point in time. Each change returns a new state, which maintains the integrity of the model between changes.

It’s also easier to test because the data is consistent and predictable.

We can create a Reactive form as follows:

app.module.ts :

import { BrowserModule } from "@angular/platform-browser";  
import { NgModule } from "@angular/core";  
import { ReactiveFormsModule } from "@angular/forms";  
import { AppComponent } from "./app.component";

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

app.component.ts :

import { Component } from "@angular/core";  
import { FormControl } from "@angular/forms";

@Component({  
  selector: "app-root",  
  templateUrl: "./app.component.html",  
  styleUrls: ["./app.component.css"]  
})  
export class AppComponent {  
  nameControl = new FormControl("");  
}

app.component.html :

<input type="text" [formControl]="nameControl" />  
<p>{{ nameControl.value }}</p>

In the code above, we imported the ReactiveFormsModule in app.module.ts .

Then in AppComponent , we added a FormControl called nameControl .

Then we connect our input element to nameControl by using the formControl property.

To display the value we typed in, we reference the nameControl ‘s value property as we did with the p element.

Replacing a Form Control Value

We can call the setValue method on a FormControl to replace the value of it.

For example, we can write the following code:

app.component.ts

import { Component } from "@angular/core";  
import { FormControl } from "@angular/forms";

@Component({  
  selector: "app-root",  
  templateUrl: "./app.component.html",  
  styleUrls: ["./app.component.css"]  
})  
export class AppComponent {  
  nameControl = new FormControl(""); 

  updateName() {  
    this.nameControl.setValue("Jane");  
  }  
}

app.component.html :

<input type="text" [formControl]="nameControl" />  
<button (click)="updateName()">Update Name</button>

In the code above, we have the updateName method which calls setValue to set the value of FormControl .

When we click the button, we’ll see Jane entered in the input.

Grouping Form Controls

We can create a FormGroup to group form controls together.

For example, we can use it as follows:

app.component.ts :

import { Component } from "@angular/core";  
import { FormControl, FormGroup } from "@angular/forms";

@Component({  
  selector: "app-root",  
  templateUrl: "./app.component.html",  
  styleUrls: ["./app.component.css"]  
})  
export class AppComponent {  
  personForm = new FormGroup({  
    nameControl: new FormControl("")  
  });  
}

app.component.html :

<form [formGroup]="personForm">  
  <input type="text" formControlName="nameControl" />  
</form>

We bound the form to personForm by using the formGroup property.

Then we set the form control in the form group by using the formControlName property.

Submitting Form Data

We can submit data entered into a Reactive form by attaching an onSubmit handler to our form.

To do that we can write the following:

app.component.ts :

import { Component } from "@angular/core";  
import { FormControl, FormGroup } from "@angular/forms";

@Component({  
  selector: "app-root",  
  templateUrl: "./app.component.html",  
  styleUrls: ["./app.component.css"]  
})  
export class AppComponent {  
  personForm = new FormGroup({  
    nameControl: new FormControl("")  
  }); onSubmit() {  
    console.log(this.personForm.value);  
  }  
}

app.component.html :

<form [formGroup]="personForm" (ngSubmit)="onSubmit()">  
  <input type="text" formControlName="nameControl" />  
  <button type="submit">Submit</button>  
</form>

In the code above, we have the onSubmit handler, which gets the value of all the fields entered by accessing the value property of the form group.

When we click Submit, we should see what we typed in.

To disable the Submit button if the form isn’t valid, we can write:

app.component.html:

<button type="submit" [disabled]="!personForm.valid">Submit</button>

to set the disabled property of the button when the personForm ‘s valid value.

Creating Nested Form Groups

We can nest form groups. For example, we can write the following code to do that:

app.component.ts :

import { Component } from "@angular/core";  
import { FormControl, FormGroup } from "@angular/forms";

@Component({  
  selector: "app-root",  
  templateUrl: "./app.component.html",  
  styleUrls: ["./app.component.css"]  
})  
export class AppComponent {  
  personForm = new FormGroup({  
    name: new FormControl(""),  
    address: new FormGroup({  
      street: new FormControl("")  
    })  
  }); onSubmit() {  
    console.log(this.personForm.value);  
  }  
}

app.component.html :

<form [formGroup]="personForm" (ngSubmit)="onSubmit()">  
  <input type="text" formControlName="name" placeholder="Name" />  
  <div formGroupName="address">  
    <input type="text" formControlName="street" placeholder="Street" />  
  </div>  
  <button type="submit">Submit</button>  
</form>

In the code above, we have the personForm form group with the name FormControl in the root.

Then we added the address FormGroup , which has the street FormControl inside.

In app.component.html , we bind the form to the personForm FormGroup as usual, but we have an extra div to bind the div and what’s inside to the address FormGroup .

Then we bind the street FormControl to our input inside.

Conclusion

We can create FormControl s and bind input elements to them.

Also, we can create FormGroup s and bind forms to them.

FormGroup s can be nested within each other.

We can access a FormGroup and FormControl ‘s values with the value property.

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