Form submission handling in Angular - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to bind the form submission to the handler method.

Angular

<form ([1])="onSubmit()">
  <button type="submit">Submit</button>
</form>

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

AngSubmit

Bsubmit

Cclick

Dchange

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'click' event on the form tag instead of 'ngSubmit'.

Using 'submit' event which is native but Angular prefers 'ngSubmit'.

The ngSubmit event binds the form submission to the handler method in Angular.

2fill in blank

medium

Complete the code to prevent the default form submission behavior.

Angular

onSubmit(event: Event) {
  event.[1]();
  console.log('Form submitted');
}

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

AstopPropagation

BdetachEvent

CstopImmediatePropagation

DpreventDefault

Attempts:

3 left

💡 Hint

Common Mistakes

Using stopPropagation which only stops event bubbling.

Using stopImmediatePropagation which is not needed here.

Calling preventDefault() stops the browser from performing the default form submission, allowing Angular to handle it.

3fill in blank

hard

Fix the error in the form control binding to correctly update the model.

Angular

<input type="text" [[1]]="name" (ngModelChange)="name=$event" />

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

AformControlName

Bvalue

CngModel

DformControl

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'value' which is one-way binding only.

Using 'formControl' or 'formControlName' without importing ReactiveFormsModule.

Using [ngModel] binds the input to the component's property for two-way data binding.

4fill in blank

hard

Fill both blanks to create a reactive form with a control named 'email'.

Angular

this.form = new Form[1]({
  email: new Form[2]('')
});

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

AGroup

BControl

CArray

DBuilder

Attempts:

3 left

💡 Hint

Common Mistakes

Using FormArray instead of FormGroup for a single form.

Confusing FormBuilder with FormControl.

FormGroup groups controls, and FormControl creates a single control.

5fill in blank

hard

Fill all three blanks to handle form submission and reset the form.

Angular

onSubmit() {
  if (this.form.[1] === 'VALID') {
    console.log(this.form.[2]);
    this.form.[3]();
  }
}

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

Astatus

Bvalue

Creset

Dcontrols

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'controls' instead of 'status' to check validity.

Trying to reset form by setting value to empty instead of calling reset().

Using status === 'VALID' to check validity, value gets the form data, and reset() clears the form.

Practice

1. What is the purpose of the (ngSubmit) directive in Angular forms?

easy

A. It binds the form inputs to component properties.

B. It listens for the form's submit event and triggers a handler function.

C. It disables the submit button when the form is invalid.

D. It styles the form elements automatically.

Solution

1. Step 1: Understand the role of (ngSubmit)

   The (ngSubmit) directive listens for the submit event on a form element in Angular.

2. Step 2: Identify what happens on submit

   When the form is submitted, (ngSubmit) triggers the specified handler function in the component.

3. Final Answer:

   It listens for the form's submit event and triggers a handler function. -> Option B

4. Quick Check:

   (ngSubmit) handles form submission event [OK]

Hint: Remember (ngSubmit) triggers code on form submit [OK]

Common Mistakes:

• Confusing (ngSubmit) with input binding
• Thinking (ngSubmit) disables buttons
• Assuming (ngSubmit) styles forms

2. Which of the following is the correct syntax to bind an input field to a component property named username using two-way binding in Angular?

easy

A.

B.

C.

D.

Solution

1. Step 1: Recall two-way binding syntax

   Angular uses [(ngModel)] for two-way data binding on form inputs.

2. Step 2: Match syntax to property

   The correct syntax to bind username is <input [(ngModel)]="username">.

3. Final Answer:

   <input [(ngModel)]="username"> -> Option A

4. Quick Check:

   Two-way binding = [(ngModel)] [OK]

Hint: Two-way binding always uses [(ngModel)] [OK]

Common Mistakes:

• Using only [ngModel] without parentheses
• Using (ngModelChange) alone without brackets
• Confusing event binding with property binding

3. Given the following Angular template snippet, what will be the value of submittedName after the form is submitted?

<form (ngSubmit)="submitForm()" #myForm="ngForm">
  <input name="name" [(ngModel)]="userName" required>
  <button type="submit" [disabled]="myForm.invalid">Submit</button>
</form>

And the component code:

userName = '';
submittedName = '';

submitForm() {
  this.submittedName = this.userName;
}

If the user types "Alice" and submits, what is submittedName?

medium

A. undefined

B. "" (empty string)

C. "Alice"

D. null

Solution

1. Step 1: Understand two-way binding effect

   The input field binds userName with two-way binding, so typing "Alice" updates userName to "Alice".

2. Step 2: Check submitForm behavior

   On submit, submitForm() sets submittedName to the current userName, which is "Alice".

3. Final Answer:

   "Alice" -> Option C

4. Quick Check:

   Two-way binding updates userName, submitForm copies it [OK]

Hint: Two-way binding updates property before submit [OK]

Common Mistakes:

• Assuming submittedName stays empty
• Confusing variable names
• Ignoring two-way binding effect

4. Identify the error in this Angular form submission code snippet:

<form (ngSubmit)="onSubmit">
  <input [(ngModel)]="email" name="email" required>
  <button type="submit">Send</button>
</form>

Component method:

onSubmit() {
  console.log('Form submitted:', this.email);
}

medium

A. The (ngSubmit) should be (ngSubmit)="onSubmit()" with parentheses.

B. The input is missing a type attribute.

C. The button should have [disabled]="form.invalid".

D. The name attribute on input is not needed.

Solution

1. Step 1: Check (ngSubmit) syntax

   The (ngSubmit) directive requires a function call with parentheses to execute the method on submit.

2. Step 2: Identify the missing parentheses

   Using (ngSubmit)="onSubmit" passes the function reference but does not call it; it should be (ngSubmit)="onSubmit()".

3. Final Answer:

   The (ngSubmit) should be (ngSubmit)="onSubmit()" with parentheses. -> Option A

4. Quick Check:

   Call handler with () in (ngSubmit) [OK]

Hint: Always add () to call function in (ngSubmit) [OK]

Common Mistakes:

• Omitting parentheses in (ngSubmit)
• Ignoring required name attribute
• Thinking input type is mandatory for submission

5. You want to disable the submit button in an Angular form until all required fields are valid. Which approach correctly implements this behavior?

<form (ngSubmit)="submit()" #myForm="ngForm">
  <input name="email" [(ngModel)]="email" required>
  <input name="password" [(ngModel)]="password" required minlength="6">
  <button type="submit" ???>Submit</button>
</form>

What should replace ??? to disable the button when the form is invalid?

hard

A. [disabled]="email === '' || password.length < 6"

B. [disabled]="myForm.valid"

C. [disabled]="false"

D. [disabled]="myForm.invalid"

Solution

1. Step 1: Understand Angular form validity

   The template reference variable myForm exposes the form's validity state via myForm.invalid and myForm.valid.

2. Step 2: Use form invalid property to disable button

   Setting [disabled]="myForm.invalid" disables the submit button until the form is valid.

3. Final Answer:

   [disabled]="myForm.invalid" -> Option D

4. Quick Check:

   Disable button when form.invalid is true [OK]

Hint: Use form.invalid to disable submit button [OK]

Common Mistakes:

• Using negation incorrectly with valid property
• Manually checking fields instead of form state
• Setting disabled to false always