Pipe chaining in Angular - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Angular template with pipe chaining?

Given the component property name = 'Angular', what will be displayed by this template?

<div>{{ name | lowercase | slice:0:4 | uppercase }}</div>

A ANGU

B angu

C ANGULAR

D anguL

💡 Hint

Remember that pipes are applied from left to right, and each pipe transforms the output of the previous one.

The lowercase pipe converts 'Angular' to 'angular'. Then slice:0:4 extracts 'angu'. Finally, uppercase converts it to 'ANGU'.

📝 Syntax

intermediate

Which option correctly chains pipes to format a date and then uppercase it?

Assuming today = new Date('2024-06-15'), which template expression correctly formats the date as 'Jun 15, 2024' and then converts it to uppercase?

A {{ today | date:'MMM d, y' | toUpperCase }}

B {{ today | date:'MMM d, y' | uppercase }}

C {{ today | uppercase | date:'MMM d, y' }}

D {{ today | date:'MMM d, y' | uppercase() }}

💡 Hint

Pipes are chained left to right. The uppercase pipe works on strings, so it must come after the date pipe.

Option B correctly formats the date first, then uppercases the string. Option B tries to uppercase a Date object, which fails. Options A and D use invalid pipe syntax.

🔧 Debug

advanced

What happens with this pipe chaining when value is null?

Given value = null, what happens with this template?

<div>{{ value | uppercase | slice:0:3 }}</div>

A No error, outputs empty string

B TypeError: Cannot read property 'toString' of null

C SyntaxError: Unexpected token ':'

D Runtime error: slice is not a function

💡 Hint

Angular built-in pipes like uppercase and slice handle null safely without throwing errors.

No error occurs. The uppercase pipe returns null for null input, and the slice pipe returns an empty string.

❓ state_output

advanced

What is the displayed output after changing component state?

Component code:

name = 'Angular';
changeName() { this.name = 'Framework'; }

Template:

<div>{{ name | slice:0:4 | uppercase }}</div>
<button (click)="changeName()">Change</button>

What is shown before and after clicking the button?

A Before: ANGULAR, After: FRAME

B Before: ANGU, After: ANGU

C Before: ANGU, After: FRAM

D Before: ANGU, After: FRAME

💡 Hint

Remember slice:0:4 takes first 4 characters, and uppercase converts to uppercase.

Initially, 'Angular' sliced to 'Angu' then uppercased to 'ANGU'. After changing to 'Framework', sliced to 'Fram' then uppercased to 'FRAM'.

🧠 Conceptual

expert

Why is pipe chaining order important in Angular templates?

Consider these two expressions:

1. {{ text | lowercase | slice:0:3 }}
2. {{ text | slice:0:3 | lowercase }}

Which statement is true?

A They always produce the same output regardless of order.

B Pipes can only be chained if they are of the same type.

C Angular automatically optimizes pipe order to produce correct output.

D Order matters because each pipe transforms the input for the next pipe.

💡 Hint

Think about how the output of one pipe becomes the input of the next.

Pipe chaining applies pipes left to right. Changing order changes intermediate values, so output can differ.

Practice

1. What does pipe chaining in Angular templates allow you to do?

easy

A. Create multiple services at once

B. Run multiple components in sequence

C. Bind multiple events to a single element

D. Apply multiple pipes one after another to transform data

Solution

1. Step 1: Understand what pipes do in Angular

   Pipes transform data in templates to change how it looks.

2. Step 2: Understand pipe chaining

   Pipe chaining means applying several pipes in a row, where each pipe uses the previous pipe's output.

3. Final Answer:

   Apply multiple pipes one after another to transform data -> Option D

4. Quick Check:

   Pipe chaining = multiple pipes applied in sequence [OK]

Hint: Remember pipes transform data; chaining applies many in order [OK]

Common Mistakes:

• Confusing pipes with components or services
• Thinking pipes run in parallel instead of sequence
• Believing pipe chaining changes event bindings

2. Which of the following is the correct syntax for chaining pipes in an Angular template?

easy

A. {{ value | pipe1 | pipe2 }}

B. {{ value | pipe1, pipe2 }}

C. {{ value | pipe1; pipe2 }}

D. {{ value | pipe1 & pipe2 }}

Solution

1. Step 1: Recall Angular pipe chaining syntax

   Angular uses the pipe symbol | to chain pipes in templates.

2. Step 2: Identify correct chaining format

   Multiple pipes are chained by repeating | pipeName after the value.

3. Final Answer:

   {{ value | pipe1 | pipe2 }} -> Option A

4. Quick Check:

   Pipe chaining uses multiple | symbols [OK]

Hint: Use multiple | symbols to chain pipes [OK]

Common Mistakes:

• Using commas or semicolons instead of pipe symbols
• Trying to chain pipes with & or other operators
• Missing the pipe symbol between pipes

3. Given the Angular template code:
{{ 'angular' | uppercase | slice:0:3 }}
What will be the displayed output?

medium

A. ANG

B. ang

C. ANGULAR

D. angul

Solution

1. Step 1: Apply the first pipe uppercase

   The string 'angular' becomes 'ANGULAR'.

2. Step 2: Apply the second pipe slice:0:3

   Slice takes characters from index 0 up to (but not including) 3, so 'ANG'.

3. Final Answer:

   ANG -> Option A

4. Quick Check:

   Uppercase then slice = 'ANG' [OK]

Hint: Apply pipes left to right, each uses previous output [OK]

Common Mistakes:

• Applying slice before uppercase
• Confusing slice end index as inclusive
• Expecting lowercase output

4. What is wrong with this Angular template expression?
{{ 123 | uppercase | slice:0:2 }}

medium

A. Numbers cannot be used with pipes

B. There is no error; this works fine

C. The uppercase pipe cannot be applied to a number

D. The slice pipe requires a string input

Solution

1. Step 1: Check the first pipe uppercase usage

   Angular's uppercase pipe coerces the input to a string first (123 becomes '123'), then applies toUpperCase(), resulting in '123'.

2. Step 2: Apply the second pipe slice:0:2

   On '123', slice from 0 to 2 gives '12'. No error occurs.

3. Final Answer:

   There is no error; this works fine -> Option B

4. Quick Check:

   Uppercase coerces number to string, then slice works [OK]

Hint: Angular pipes like uppercase coerce non-strings to string [OK]

Common Mistakes:

• Thinking uppercase strictly requires string input without coercion
• Believing numbers cause runtime errors in pipes
• Assuming slice would fail due to input type

5. You want to display a user's name in uppercase but only show the first 5 characters. Which pipe chaining expression correctly achieves this in Angular?

hard

A. {{ userName | uppercase, slice:0:5 }}

B. {{ userName | slice:0:5 | uppercase }}

C. {{ userName | uppercase | slice:0:5 }}

D. {{ userName | slice:5 | uppercase }}

Solution

1. Step 1: Understand the desired output

   The name should be fully uppercase, then only the first 5 characters shown.

2. Step 2: Determine correct pipe order

   First apply uppercase to convert all letters, then slice:0:5 to get first 5 characters.

3. Step 3: Check options for correct syntax and order

   {{ userName | uppercase | slice:0:5 }} applies uppercase first, then slice, which matches the requirement.

4. Final Answer:

   {{ userName | uppercase | slice:0:5 }} -> Option C

5. Quick Check:

   Uppercase then slice = correct order [OK]

Hint: Uppercase first, then slice to get correct output [OK]

Common Mistakes:

• Slicing before uppercase changes output
• Using commas instead of pipes
• Wrong slice parameters