Template reference variables in Angular - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a template reference variable named 'inputRef' on the input element.

Angular

<input type="text" [1]="inputRef">

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

A$

B*

C#

D@

Attempts:

3 left

💡 Hint

Common Mistakes

Using '*' instead of '#' to declare the variable.

Forgetting the symbol and just writing the variable name.

Using '@' or '$' which are not valid for template references.

In Angular templates, the '#' symbol is used to declare a template reference variable.

2fill in blank

medium

Complete the code to access the value of the input using the template reference variable 'inputRef'.

Angular

<button (click)="onClick([1].value)">Submit</button>

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

ArefInput

BinputRef

Cthis.inputRef

Dinput

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'this.inputRef' which is invalid in templates.

Using a different variable name than declared.

Using the element tag name instead of the reference variable.

The template reference variable 'inputRef' can be used directly in the template to access the input element's properties.

3fill in blank

hard

Fix the error in the code to correctly bind the input value to the component method using the template reference variable 'myInput'.

Angular

<input #myInput type="text">
<button (click)="submit([1])">Send</button>

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

AmyInput.value

BmyInput

CmyInput.text

DmyInput.input

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the whole element instead of its value.

Using incorrect property names like 'text' or 'input'.

To get the current value of the input element, use 'myInput.value'.

4fill in blank

hard

Fill both blanks to declare a template reference variable 'box' on a div and use it to change its background color on button click.

Angular

<div [1]="box" style="width:100px; height:100px;"></div>
<button (click)="box.style.backgroundColor = '[2]'">Change Color</button>

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

A#

B*

Cred

Dblue

Attempts:

3 left

💡 Hint

Common Mistakes

Using '*' instead of '#' for the variable.

Using invalid color names or missing quotes.

Use '#' to declare the template reference variable and 'red' as the color to change the background.

5fill in blank

hard

Fill all three blanks to create a template reference variable 'inputBox', bind its value to a paragraph, and clear the input on button click.

Angular

<input type="text" [1]="inputBox">
<p>[2].value</p>
<button (click)="[3].value = ''">Clear</button>

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

A#

BinputBox

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using '*' instead of '#' to declare the variable.

Using different variable names inconsistently.

Trying to clear the input with incorrect syntax.

Declare the variable with '#', then use 'inputBox' to access its value and clear it.

Practice

1. What is the purpose of a template reference variable in Angular templates?

easy

A. To create a service for dependency injection

B. To define a new Angular component

C. To access a DOM element or component instance directly in the template

D. To write CSS styles inside the template

Solution

1. Step 1: Understand what template reference variables do

   They let you refer to elements or components inside the template without extra code in the component class.

2. Step 2: Identify the correct purpose

   Accessing DOM elements or component instances directly in the template is exactly what template reference variables do.

3. Final Answer:

   To access a DOM element or component instance directly in the template -> Option C

4. Quick Check:

   Template reference variable = direct template access [OK]

Hint: Remember: #variableName points to element/component [OK]

Common Mistakes:

• Confusing template reference variables with component or service creation
• Thinking they are used for styling or CSS
• Assuming they are for dependency injection

2. Which of the following is the correct syntax to declare a template reference variable named inputBox on an <input> element?

easy

A.

B.

C.

D.

Solution

1. Step 1: Recall Angular template reference variable syntax

   Angular uses the #variableName syntax to declare template reference variables.

2. Step 2: Match the syntax to the options

   Only uses #inputBox which is correct.

3. Final Answer:

   <input #inputBox> -> Option A

4. Quick Check:

   #variableName syntax = correct declaration [OK]

Hint: Use # before name to declare template reference variable [OK]

Common Mistakes:

• Using ref, var, or let which are not Angular template reference syntax
• Confusing Angular syntax with other frameworks
• Missing the # symbol

3. Given the template snippet:

<input #myInput type="text">
<button (click)="alert(myInput.value)">Show Value</button>

What happens when the button is clicked after typing "Hello" in the input?

medium

A. An alert box shows the text "Hello"

B. An alert box shows the text "myInput"

C. Nothing happens because myInput is undefined

D. A runtime error occurs

Solution

1. Step 1: Understand the template reference variable usage

   The #myInput variable refers to the input element. Accessing myInput.value gets the current text typed.

2. Step 2: Analyze the button click event

   Clicking the button calls alert(myInput.value), so it shows the input's current value.

3. Final Answer:

   An alert box shows the text "Hello" -> Option A

4. Quick Check:

   myInput.value alerts typed text [OK]

Hint: Template ref variable .value gets input content [OK]

Common Mistakes:

• Thinking myInput is a string instead of element reference
• Assuming myInput is undefined or inaccessible
• Expecting no action or error on click

4. Consider this template code:

<input #userInput type="text">
<button (click)="logValue()">Log</button>

And component code:

logValue() {
  console.log(userInput.value);
}

What is the problem here?

medium

A. The template reference variable should be declared with $ sign

B. userInput is not defined in the component class, causing an error

C. logValue() should be an arrow function

D. There is no problem; it works fine

Solution

1. Step 1: Identify scope of template reference variables

   Template reference variables exist only in the template, not in the component class.

2. Step 2: Check component method usage

   The method tries to access userInput directly, which is undefined in the class, causing an error.

3. Final Answer:

   userInput is not defined in the component class, causing an error -> Option B

4. Quick Check:

   Template refs not accessible in class directly [OK]

Hint: Template refs only work inside template, not class methods [OK]

Common Mistakes:

• Trying to use template refs inside component class directly
• Thinking template refs need $ or other symbols
• Assuming arrow functions fix scope issues

5. How can you use a template reference variable to reset an input field's value to empty when clicking a button?

<input #myInput type="text">
<button (click)="???">Reset</button>

Which is the correct replacement for ????

hard

A. this.myInput.value = ''

B. myInput.reset()

C. reset(myInput)

D. myInput.value = ''

Solution

1. Step 1: Understand template reference variable usage in event binding

   You can directly access the element via the variable and set its properties in the template expression.

2. Step 2: Choose the correct syntax to clear input value

   Setting myInput.value = '' clears the input. Using this or calling reset() method is incorrect here.

3. Final Answer:

   myInput.value = '' -> Option D

4. Quick Check:

   Directly assign empty string to .value to reset [OK]

Hint: Assign empty string to .value on template ref to clear input [OK]

Common Mistakes:

• Using this.myInput which is undefined in template
• Calling reset() which input element does not have
• Trying to call a function reset() without defining it