FormGroup for grouping controls in Angular - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a FormGroup named 'profileForm'.

Angular

profileForm = new FormGroup([1]);

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

A['firstName', 'lastName']

BFormControl

Cnew FormControl('')

D{firstName: new FormControl(''), lastName: new FormControl('')}

Attempts:

3 left

💡 Hint

Common Mistakes

Passing an array instead of an object.

Passing a single FormControl instead of an object of controls.

The FormGroup constructor expects an object with keys as control names and values as FormControl instances.

2fill in blank

medium

Complete the code to import the necessary Angular forms class for using FormGroup.

Angular

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

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

AFormsModule

BReactiveFormsModule

CFormGroup

DNgForm

Attempts:

3 left

💡 Hint

Common Mistakes

Importing FormsModule instead of FormGroup.

Importing ReactiveFormsModule which is a module, not the class.

You need to import FormGroup from @angular/forms to create form groups.

3fill in blank

hard

Fix the error in the code to correctly access the 'firstName' control value from the FormGroup.

Angular

const firstNameValue = this.profileForm.get([1]).value;

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

A'firstName'

BfirstName

C['firstName']

Dthis.firstName

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the control name without quotes causes runtime errors.

Using array syntax or this keyword incorrectly.

The get method expects the control name as a string, so it must be quoted.

4fill in blank

hard

Fill both blanks to create a FormGroup with controls 'email' and 'password' initialized with empty strings.

Angular

loginForm = new FormGroup({ [1]: new FormControl(''), [2]: new FormControl('') });

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

Aemail

Bpassword

Cusername

Duser

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect control names like 'username' or 'user'.

Not using string keys for controls.

The keys in the object passed to FormGroup are the control names. Here, they are 'email' and 'password'.

5fill in blank

hard

Fill all three blanks to create a FormGroup named 'addressForm' with controls 'street', 'city', and 'zipCode' initialized with empty strings.

Angular

addressForm = new FormGroup({ [1]: new FormControl(''), [2]: new FormControl(''), [3]: new FormControl('') });

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

Astreet

Bcity

CzipCode

Dstate

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong control names.

Forgetting to separate keys with commas.

The object keys are the control names: 'street', 'city', and 'zipCode'.

Practice

1. What is the main purpose of using FormGroup in Angular forms?

easy

A. To group related form controls for easier management

B. To style form controls with CSS

C. To fetch data from a server

D. To create animations in forms

Solution

1. Step 1: Understand what FormGroup does

   FormGroup groups multiple form controls together so they can be managed as one unit.

2. Step 2: Compare options with FormGroup purpose

   Only To group related form controls for easier management describes grouping controls for easier management, which is the core use of FormGroup.

3. Final Answer:

   To group related form controls for easier management -> Option A

4. Quick Check:

   FormGroup groups controls = A [OK]

Hint: FormGroup groups controls logically for easier handling [OK]

Common Mistakes:

• Confusing FormGroup with styling or data fetching
• Thinking FormGroup creates animations
• Assuming FormGroup is for server communication

2. Which of the following is the correct way to create a FormGroup with two controls named 'firstName' and 'lastName' in Angular?

easy

A. new FormControl({ firstName: '', lastName: '' })

B. new FormGroup({ firstName: new FormControl(''), lastName: new FormControl('') })

C. new FormGroup(['firstName', 'lastName'])

D. new FormArray([new FormControl('firstName'), new FormControl('lastName')])

Solution

1. Step 1: Recall FormGroup syntax

   FormGroup takes an object with keys as control names and values as FormControl instances.

2. Step 2: Check each option

   new FormGroup({ firstName: new FormControl(''), lastName: new FormControl('') }) correctly creates a FormGroup with two FormControls. Options B, C, and D use wrong classes or structures.

3. Final Answer:

   new FormGroup({ firstName: new FormControl(''), lastName: new FormControl('') }) -> Option B

4. Quick Check:

   FormGroup needs object of FormControls = A [OK]

Hint: FormGroup uses object with FormControl instances [OK]

Common Mistakes:

• Using FormControl instead of FormGroup for multiple controls
• Passing array instead of object to FormGroup
• Confusing FormArray with FormGroup

3. Given this Angular code snippet, what will console.log(this.profileForm.value) output?

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

medium

A. undefined

B. ['Alice', 'Smith']

C. { value: { firstName: 'Alice', lastName: 'Smith' } }

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

Solution

1. Step 1: Understand FormGroup value property

   The value property returns an object with keys as control names and values as their current values.

2. Step 2: Check the given controls and values

   Controls are firstName and lastName with values 'Alice' and 'Smith'. So value is { firstName: 'Alice', lastName: 'Smith' }.

3. Final Answer:

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

4. Quick Check:

   FormGroup.value returns object of control values = D [OK]

Hint: FormGroup.value returns object with control names and values [OK]

Common Mistakes:

• Expecting an array instead of object
• Thinking value wraps inside another object
• Assuming value is undefined before form submission

4. Identify the error in this Angular code that tries to create a FormGroup:

this.userForm = new FormGroup({
  username: FormControl('user1'),
  email: new FormControl('[e-mail]')
});

medium

A. 'FormControl' must be called with 'new' keyword for 'username' control

B. 'FormGroup' should be 'FormArray' instead

C. 'email' control should not have initial value

D. No error, code is correct

Solution

1. Step 1: Check how FormControl is instantiated

   FormControl must be created with 'new' keyword. 'username' control misses 'new'.

2. Step 2: Verify other controls and FormGroup usage

   'email' control is correct. FormGroup is correct for grouping controls.

3. Final Answer:

   'FormControl' must be called with 'new' keyword for 'username' control -> Option A

4. Quick Check:

   FormControl needs 'new' keyword = B [OK]

Hint: Always use 'new' with FormControl instances [OK]

Common Mistakes:

• Omitting 'new' keyword when creating FormControl
• Confusing FormGroup with FormArray
• Thinking initial values are mandatory or forbidden

5. You want to disable all controls inside a FormGroup named settingsForm at once. Which is the correct way to do this in Angular?

hard

A. Set each control's value to null to disable them

B. Call settingsForm.controls.disable() to disable controls

C. Call settingsForm.disable() to disable all controls together

D. Use settingsForm.setValue(null) to disable controls

Solution

1. Step 1: Understand FormGroup disable method

   FormGroup has a disable() method that disables all child controls at once.

2. Step 2: Check other options for disabling controls

   Call settingsForm.controls.disable() to disable controls is invalid because controls is an object, not a method. Options A and D do not disable controls but change values.

3. Final Answer:

   Call settingsForm.disable() to disable all controls together -> Option C

4. Quick Check:

   FormGroup.disable() disables all controls = C [OK]

Hint: Use FormGroup.disable() to disable all controls at once [OK]

Common Mistakes:

• Trying to disable controls by setting values to null
• Calling disable on controls object directly
• Using setValue to disable controls