Why forms matter in Angular - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the FormsModule needed for template-driven forms in Angular.

Angular

import { [1] } from '@angular/forms';

Drag options to blanks, or click blank then click option'

ACommonModule

BHttpClientModule

CRouterModule

DFormsModule

Attempts:

3 left

💡 Hint

Common Mistakes

Importing HttpClientModule instead of FormsModule

Forgetting to import any module

Importing RouterModule by mistake

The FormsModule is required to use template-driven forms in Angular.

2fill in blank

medium

Complete the code to bind the input field to the component property using two-way binding.

Angular

<input [(ngModel)]="[1]" name="username">

Drag options to blanks, or click blank then click option'

Auser

BuserName

Cusername

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using a property name that does not exist in the component

Forgetting to add the name attribute

Using one-way binding instead of two-way binding

The property username is bound to the input using [(ngModel)] for two-way binding.

3fill in blank

hard

Fix the error in the form submission method to prevent default behavior.

Angular

<form (ngSubmit)="[1]($event)">

Drag options to blanks, or click blank then click option'

AonSubmit

BhandleSubmit

CsubmitForm

Dsubmit

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method name not defined in the component

Not passing the event parameter

Not preventing default form submission

The method onSubmit is commonly used to handle form submission and can receive the event to prevent default behavior.

4fill in blank

hard

Fill both blanks to create a reactive form control and bind it in the template.

Angular

this.form = new FormGroup({ name: new [1]('') });

<input [formControl]="this.form.get('[2]')">

Drag options to blanks, or click blank then click option'

AFormControl

BFormGroup

Cname

Dusername

Attempts:

3 left

💡 Hint

Common Mistakes

Using FormGroup instead of FormControl for a single control

Mismatching the control name in the template

Forgetting to initialize the form control

FormControl creates a control for the form field, and the control is accessed by its name name in the template.

5fill in blank

hard

Fill all three blanks to add validation and check if the form control is valid.

Angular

this.form = new FormGroup({
  email: new FormControl('', [[1].required, [2].email])
});

const isValid = this.form.get('email')?.[3];

Drag options to blanks, or click blank then click option'

AValidators

BFormsModule

Cvalid

DFormControl

Attempts:

3 left

💡 Hint

Common Mistakes

Using FormsModule instead of Validators for validation

Checking the wrong property for validity

Not importing Validators

Validators provides built-in validation functions like required and email. The valid property checks if the control passes validation.

Practice

1. Why are forms important in Angular applications?

easy

A. They allow users to input and send data to the app.

B. They automatically style the app without CSS.

C. They replace the need for components.

D. They make the app run faster without code changes.

Solution

1. Step 1: Understand the role of forms in apps

   Forms collect user input, which is essential for interactive apps.

2. Step 2: Connect to Angular's form handling

   Angular uses forms to manage and validate user data before processing.

3. Final Answer:

   They allow users to input and send data to the app. -> Option A

4. Quick Check:

   Forms collect user data [OK]

Hint: Forms handle user input and data submission [OK]

Common Mistakes:

• Thinking forms only style the app
• Believing forms replace components
• Assuming forms speed up app without code

2. Which of the following is the correct way to create a form control in Angular?

easy

A. const name = new FormControl('');

B. const name = FormControl();

C. const name = new formcontrol('');

D. const name = FormGroup('');

Solution

1. Step 1: Recall Angular form control syntax

   FormControl is a class and must be instantiated with 'new'.

2. Step 2: Check capitalization and usage

   Correct syntax uses 'new FormControl('')', with capital F and C.

3. Final Answer:

   const name = new FormControl(''); -> Option A

4. Quick Check:

   FormControl requires 'new' keyword [OK]

Hint: Use 'new FormControl()' with capital letters [OK]

Common Mistakes:

• Omitting 'new' keyword
• Using wrong capitalization
• Confusing FormControl with FormGroup

3. Given this Angular form setup:

this.profileForm = new FormGroup({
  firstName: new FormControl(''),
  lastName: new FormControl('')
});
console.log(this.profileForm.value);

What will be logged to the console right after this code runs?

medium

A. { firstName: null, lastName: null }

B. undefined

C. null

D. { firstName: '', lastName: '' }

Solution

1. Step 1: Understand FormGroup initial values

   Each FormControl is initialized with an empty string ''.

2. Step 2: Check the value property of FormGroup

   FormGroup.value returns an object with keys and their current values.

3. Final Answer:

   { firstName: '', lastName: '' } -> Option D

4. Quick Check:

   FormGroup.value returns empty strings object [OK]

Hint: FormGroup.value shows current control values as object [OK]

Common Mistakes:

• Expecting null or undefined instead of empty strings
• Confusing FormGroup.value with FormControl instance
• Assuming console logs FormGroup object directly

4. What is wrong with this Angular form code?

this.loginForm = new FormGroup({
  email: FormControl(''),
  password: new FormControl('')
});

medium

A. FormGroup cannot have more than one control.

B. FormControl cannot be used inside FormGroup.

C. Missing 'new' keyword before FormControl for email control.

D. Password control should be FormGroup, not FormControl.

Solution

1. Step 1: Check syntax for creating FormControl instances

   Each FormControl must be created with 'new FormControl()'.

2. Step 2: Identify the error in email control

   Email control is missing 'new', causing a syntax/runtime error.

3. Final Answer:

   Missing 'new' keyword before FormControl for email control. -> Option C

4. Quick Check:

   Every FormControl needs 'new' [OK]

Hint: Remember 'new' before every FormControl instance [OK]

Common Mistakes:

• Omitting 'new' keyword
• Thinking FormGroup limits controls to one
• Confusing FormControl and FormGroup roles

5. You want to create a form that requires a user to enter a non-empty email and password. Which Angular approach best ensures the form is valid only when both fields are filled?

hard

A. Use only FormControl for email and ignore password validation.

B. Use FormGroup with FormControls and add Validators.required to each control.

C. Use FormGroup without validators and check values manually after submit.

D. Use FormGroup with empty FormControls and no validation.

Solution

1. Step 1: Understand Angular validation

   Validators.required ensures a control is not empty and marks form invalid if empty.

2. Step 2: Apply validators to both email and password controls

   Adding Validators.required to both controls enforces non-empty input before form is valid.

3. Step 3: Compare other options

   Manual checks or missing validators do not enforce form validity automatically.

4. Final Answer:

   Use FormGroup with FormControls and add Validators.required to each control. -> Option B

5. Quick Check:

   Validators.required on controls = form valid only if filled [OK]

Hint: Add Validators.required to controls for mandatory fields [OK]

Common Mistakes:

• Skipping validators and relying on manual checks
• Validating only one field
• Assuming empty controls are valid