Property binding with square brackets in Angular - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to bind the src property of the img tag to the imageUrl variable.

Angular

<img [1]="imageUrl" alt="Image">

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

A(src)

B<src>

C{src}

D[src]

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses instead of square brackets.

Using curly braces or angle brackets instead of square brackets.

In Angular, property binding uses square brackets around the property name, like [src].

2fill in blank

medium

Complete the code to bind the disabled property of the button to the isDisabled variable.

Angular

<button [1]="isDisabled">Click me</button>

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

A[disabled]

B(disabled)

C{disabled}

D<disabled>

Attempts:

3 left

💡 Hint

Common Mistakes

Using event binding syntax with parentheses.

Using curly braces or angle brackets.

Use square brackets to bind the disabled property to the variable isDisabled.

3fill in blank

hard

Fix the error in the code to correctly bind the value property of the input to the userName variable.

Angular

<input [1]="userName">

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

A{value}

B(value)

C[value]

D<value>

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses which is for event binding.

Using curly braces or angle brackets.

Property binding requires square brackets around the property name, so use [value].

4fill in blank

hard

Fill both blanks to bind the title property to pageTitle and the alt property to imageAlt.

Angular

<img [1]="pageTitle" [2]="imageAlt">

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

A[title]

B(title)

C[alt]

D(alt)

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses which is for event binding.

Mixing property and event binding syntax.

Use square brackets for property binding on both title and alt properties.

5fill in blank

hard

Fill all three blanks to bind href to linkUrl, target to linkTarget, and rel to linkRel.

Angular

<a [1]="linkUrl" [2]="linkTarget" [3]="linkRel">Link</a>

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

A[href]

B[target]

C[rel]

D(href)

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses which is for event binding.

Forgetting square brackets on any property.

All three attributes use property binding with square brackets.

Practice

1. What does property binding with square brackets [] do in Angular?

easy

A. It creates a two-way data binding between component and template.

B. It binds a component property to an element property, updating the UI automatically.

C. It binds an event handler to an element event.

D. It defines a CSS class for an element.

Solution

1. Step 1: Understand property binding purpose

   Property binding connects component data to element properties, so UI updates when data changes.

2. Step 2: Differentiate from other bindings

   Event binding uses parentheses, two-way binding uses both brackets and parentheses, CSS class binding uses special syntax.

3. Final Answer:

   It binds a component property to an element property, updating the UI automatically. -> Option B

4. Quick Check:

   Property binding = UI updates from component data [OK]

Hint: Square brackets mean binding to element property [OK]

Common Mistakes:

• Confusing property binding with event binding
• Thinking it creates two-way binding
• Using it to bind CSS classes incorrectly

2. Which of the following is the correct syntax for binding the src property of an <img> tag to a component variable imageUrl?

easy

A.

B.

C.

D.

Solution

1. Step 1: Identify property binding syntax

   Property binding uses square brackets around the property name, like [src].

2. Step 2: Check correct attribute usage

   Inside quotes, use the component variable name without extra brackets or parentheses.

3. Final Answer:

   <img [src]="imageUrl"> -> Option C

4. Quick Check:

   Square brackets + variable name = correct property binding [OK]

Hint: Use [property]="variable" for property binding [OK]

Common Mistakes:

• Using interpolation {{}} inside src attribute for property binding
• Using parentheses () which are for event binding
• Putting brackets inside quotes incorrectly

3. Given this component code:

export function MyComponent() {
  const [isDisabled, setIsDisabled] = React.useState(true);
  return <button [disabled]="isDisabled">Click me</button>;
}

What will happen when this Angular template renders?

medium

A. There will be a syntax error because React code is used in Angular.

B. The button will be enabled because isDisabled is true.

C. The button will be disabled because isDisabled is true.

D. The button will ignore the disabled property and be enabled.

Solution

1. Step 1: Identify framework mismatch

   The code uses React hooks inside Angular template, which is invalid syntax in Angular.

2. Step 2: Understand Angular template rules

   Angular templates do not support React code or hooks; this causes a syntax error.

3. Final Answer:

   There will be a syntax error because React code is used in Angular. -> Option A

4. Quick Check:

   React code in Angular template = syntax error [OK]

Hint: Angular templates don't accept React code [OK]

Common Mistakes:

• Assuming React state works in Angular
• Thinking disabled attribute ignores wrong syntax
• Confusing framework syntax rules

4. What is wrong with this Angular template snippet?

<input [value]=username>

medium

A. The variable username must be a string literal.

B. Square brackets cannot be used on input elements.

C. The property name should be in parentheses, not brackets.

D. The value should be in quotes: [value]="username".

Solution

1. Step 1: Check property binding syntax

   Property binding requires the value inside quotes to be a valid expression.

2. Step 2: Identify missing quotes

   Here, username is not quoted, so Angular treats it as invalid syntax.

3. Final Answer:

   The value should be in quotes: [value]="username". -> Option D

4. Quick Check:

   Property binding expression must be quoted [OK]

Hint: Always quote expressions inside square brackets [OK]

Common Mistakes:

• Omitting quotes around binding expressions
• Using parentheses instead of brackets for property binding
• Thinking brackets can't be used on input

5. You want to disable a button dynamically based on a component boolean variable isLoading. Which Angular template code correctly disables the button when isLoading is true and enables it otherwise?

hard

A. <button [disabled]="isLoading">Submit</button>

B. <button disabled="isLoading">Submit</button>

C. <button [disabled]="!isLoading">Submit</button>

D. <button (disabled)="isLoading">Submit</button>

Solution

1. Step 1: Understand property binding for boolean attributes

   Use square brackets to bind the disabled property to the component variable.

2. Step 2: Check logic for disabling

   When isLoading is true, disabled should be true to disable the button.

3. Step 3: Evaluate options

   <button [disabled]="isLoading">Submit</button> binds disabled to isLoading correctly. <button disabled="isLoading">Submit</button> treats isLoading as string, not variable. <button [disabled]="!isLoading">Submit</button> disables when isLoading is false (wrong logic). <button (disabled)="isLoading">Submit</button> uses parentheses which is event binding, invalid here.

4. Final Answer:

   <button [disabled]="isLoading">Submit</button> -> Option A

5. Quick Check:

   Bind [disabled] to boolean variable directly [OK]

Hint: Bind [disabled] to boolean variable for dynamic enable/disable [OK]

Common Mistakes:

• Using disabled="isLoading" treats it as string
• Negating isLoading incorrectly disables button
• Using parentheses () instead of brackets []