Template expressions and statements in Angular - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What will be displayed by this Angular template expression?

Given the component property count = 5, what will this template expression show?

{{ count > 3 ? 'High' : 'Low' }}

A High

B Low

C 5

D count > 3 ? 'High' : 'Low'

💡 Hint

Check the condition inside the expression and what it returns.

The expression checks if count is greater than 3. Since 5 > 3, it returns 'High'.

📝 Syntax

intermediate

Which template expression will cause a syntax error?

Identify the Angular template expression that will cause a syntax error.

A {{ count > 5 ? 'Many' 'Few' }}

B {{ (items.length > 0) && 'Has items' }}

C {{ user?.age ?? 'Unknown' }}

D {{ user.name | uppercase }}

💡 Hint

Look for missing operators or incorrect ternary syntax.

Option A misses the colon : in the ternary operator, causing a syntax error.

❓ state_output

advanced

What is the value of message after this template statement executes?

Consider this Angular component snippet:

message = '';

What will be the value of message after clicking the button once?

A '' (empty string)

B undefined

C 'Clicked!'

D null

💡 Hint

What does the (click) event do to the message variable?

The click event sets message to 'Clicked!'.

🔧 Debug

advanced

Why does this Angular template expression cause an error?

Given the component property user = null, why does this template expression cause an error?

{{ user.name }}

A Because the expression syntax is invalid

B Because Angular does not allow dot notation in templates

C Because <code>user</code> is undefined, not null

D Because <code>user</code> is null and accessing <code>name</code> causes a runtime error

💡 Hint

Think about what happens when you try to access a property of null.

Accessing user.name when user is null causes a runtime error because null has no properties.

🧠 Conceptual

expert

Which statement about Angular template expressions and statements is correct?

Choose the correct statement about Angular template expressions and statements.

A Template expressions can contain assignments like <code>a = 5</code> but statements cannot

B Template statements can call methods and change component state, but expressions cannot

C Template expressions can include loops and conditionals like <code>for</code> and <code>if</code> statements

D Template statements are used only for displaying data, not for event handling

💡 Hint

Think about what expressions and statements are allowed to do in Angular templates.

Template expressions are for displaying data and cannot change state. Template statements handle events and can change state.

Practice

1. What is the purpose of using {{ expression }} in an Angular template?

easy

A. To display the value of the expression in the HTML

B. To run a function when a button is clicked

C. To define a new component

D. To import external stylesheets

Solution

1. Step 1: Understand template expressions

   Template expressions inside {{ }} are used to show data or values in the HTML view.

2. Step 2: Differentiate from statements

   Statements run code on events, but expressions only display values.

3. Final Answer:

   To display the value of the expression in the HTML -> Option A

4. Quick Check:

   Template expressions = display data [OK]

Hint: Remember {{ }} always shows data, not runs code [OK]

Common Mistakes:

• Confusing expressions with event handlers
• Thinking {{ }} runs functions on click
• Using {{ }} to import files

2. Which of the following is the correct syntax to bind a click event in an Angular template?

easy

A. <button <click>="doSomething()">Click</button>

B. <button (click)="doSomething()">Click</button>

C. <button [click]="doSomething()">Click</button>

D. <button {click}="doSomething()">Click</button>

Solution

1. Step 1: Recall Angular event binding syntax

   Angular uses parentheses around event names to bind events, like (click).

2. Step 2: Check each option

   Only <button (click)="doSomething()">Click</button> uses the correct (click) syntax with quotes and parentheses.

3. Final Answer:

   <button (click)="doSomething()">Click</button> -> Option B

4. Quick Check:

   Event binding uses (event) syntax [OK]

Hint: Event bindings always use parentheses (event) [OK]

Common Mistakes:

• Using square brackets instead of parentheses
• Using curly braces instead of parentheses
• Missing quotes around the method call

3. Given the component property count = 5, what will be displayed by this template snippet?
<div>Count: {{ count + 3 }}</div>

medium

A. Count: 8

B. Count: count + 3

C. Count: 53

D. Count: undefined

Solution

1. Step 1: Evaluate the expression inside {{ }}

   The expression is count + 3. Since count is 5, the expression becomes 5 + 3.

2. Step 2: Calculate the result

   5 + 3 equals 8, so the displayed text is "Count: 8".

3. Final Answer:

   Count: 8 -> Option A

4. Quick Check:

   5 + 3 = 8 [OK]

Hint: Expressions inside {{ }} calculate values immediately [OK]

Common Mistakes:

• Treating expression as a string literal
• Concatenating numbers as strings
• Expecting undefined if property missing

4. Identify the error in this Angular template snippet:
<button (click)="increment">Add</button>
Assuming the component has a method increment().

medium

A. Method name should be in double curly braces

B. Using square brackets instead of parentheses

C. Missing parentheses after method name in event binding

D. No error, syntax is correct

Solution

1. Step 1: Check event binding syntax

   The event binding calls a method on click. It should include parentheses to invoke the method, like increment().

2. Step 2: Identify the missing parentheses

   The code uses increment without parentheses, so the method won't be called.

3. Final Answer:

   Missing parentheses after method name in event binding -> Option C

4. Quick Check:

   Call methods with () in (event) bindings [OK]

Hint: Always add () to call methods in (event) bindings [OK]

Common Mistakes:

• Omitting parentheses after method name
• Using {{ }} inside event bindings
• Confusing event and property bindings

5. You want to display a user's full name in the template using {{ }}, but only if both firstName and lastName exist. Which template expression correctly shows the full name or 'Guest' if either is missing?

hard

A. {{ firstName + ' ' + lastName || 'Guest' }}

B. {{ firstName || lastName ? firstName + ' ' + lastName : 'Guest' }}

C. {{ firstName && lastName && firstName + ' ' + lastName || 'Guest' }}

D. {{ firstName && lastName ? firstName + ' ' + lastName : 'Guest' }}

Solution

1. Step 1: Understand the condition

   We want to show full name only if both firstName and lastName exist (are truthy).

2. Step 2: Analyze each option

   {{ firstName && lastName ? firstName + ' ' + lastName : 'Guest' }} uses firstName && lastName ? fullName : 'Guest', which correctly checks both exist before concatenating. Others either use OR or incorrect logic.

3. Final Answer:

   {{ firstName && lastName ? firstName + ' ' + lastName : 'Guest' }} -> Option D

4. Quick Check:

   Use && with ?: for conditional display [OK]

Hint: Use && with ?: to check both values before display [OK]

Common Mistakes:

• Using || instead of && to check both values
• Omitting the conditional operator
• Relying on || alone which may show partial names