Parameterized pipes in Angular - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to use the built-in Angular date pipe with a format parameter.

Angular

<p>{{ today | date: '[1]' }}</p>

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

A'json'

B'uppercase'

C'currency'

D'shortDate'

Attempts:

3 left

💡 Hint

Common Mistakes

Using a pipe parameter that is not a valid date format string.

Forgetting to put the format string in quotes.

The Angular date pipe formats dates. The parameter 'shortDate' shows a short date format.

2fill in blank

medium

Complete the code to use a custom pipe named 'exclaim' with a parameter for the number of exclamation marks.

Angular

<p>{{ message | exclaim: [1] }}</p>

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

A'3'

B3

Ctrue

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the number as a string with quotes.

Passing a boolean or null instead of a number.

The parameter for the custom pipe should be a number without quotes to specify how many exclamation marks to add.

3fill in blank

hard

Fix the error in the pipe usage by completing the parameter correctly.

Angular

<p>{{ price | currency: [1] }}</p>

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

A'USD'

BUSD

C100

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the currency code without quotes causing a syntax error.

Passing a number or boolean instead of a string.

The currency pipe expects the currency code as a string in quotes, like 'USD'.

4fill in blank

hard

Fill both blanks to use the Angular slice pipe with start and end parameters.

Angular

<p>{{ text | slice: [1] : [2] }}</p>

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

A2

B5

C'2'

D'5'

Attempts:

3 left

💡 Hint

Common Mistakes

Passing indexes as strings with quotes.

Using only one parameter instead of two.

The slice pipe takes numeric start and end indexes without quotes to slice the string.

5fill in blank

hard

Fill all three blanks to use a custom pipe 'repeat' with a string and a number parameter.

Angular

<p>{{ word | repeat: [1] : [2] : [3] }}</p>

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

A'! '

B3

C'- '

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Passing numbers as strings or strings as numbers.

Mixing up the order of parameters.

The custom pipe 'repeat' takes a string separator and two numbers for repetition count and spacing.

Practice

1. What is the main purpose of parameterized pipes in Angular?
{{ value | pipeName:param }}

easy

A. To define routes in the application

B. To customize how data is displayed by passing extra information

C. To handle HTTP requests

D. To create new components dynamically

Solution

1. Step 1: Understand what pipes do

   Pipes transform data in templates to display it differently.

2. Step 2: Recognize parameterized pipes

   Parameterized pipes accept extra values to customize the transformation.

3. Final Answer:

   To customize how data is displayed by passing extra information -> Option B

4. Quick Check:

   Parameterized pipes = customize display [OK]

Hint: Remember pipes change display; parameters customize it [OK]

Common Mistakes:

• Confusing pipes with components
• Thinking pipes handle logic like HTTP
• Mixing pipes with routing

2. Which of the following is the correct syntax to pass a parameter to a pipe named customPipe with parameter 5?

easy

A. {{ value | customPipe:5 }}

B. {{ value | customPipe(5) }}

C. {{ value | customPipe;5 }}

D. {{ value | customPipe->5 }}

Solution

1. Step 1: Recall Angular pipe parameter syntax

   Angular pipes use colon : to separate parameters.

2. Step 2: Check each option

   Only {{ value | customPipe:5 }} uses colon correctly: | customPipe:5.

3. Final Answer:

   {{ value | customPipe:5 }} -> Option A

4. Quick Check:

   Pipe parameters use colon : [OK]

Hint: Use colon : to pass parameters to pipes [OK]

Common Mistakes:

• Using parentheses instead of colon
• Using semicolon or arrow instead of colon
• Omitting the colon

3. Given the pipe usage {{ 1234.5678 | number:'1.2-2' }}, what will be the displayed output?

medium

A. 1234.56

B. 1234.5678

C. 1,234.57

D. 1,234.5678

Solution

1. Step 1: Understand the number pipe parameter

   The parameter '1.2-2' means minimum 1 digit before decimal, 2 minimum and 2 maximum digits after decimal.

2. Step 2: Format the number 1234.5678 accordingly

   The number is rounded to 2 decimal places and includes thousand separator: '1,234.57'.

3. Final Answer:

   1,234.57 -> Option C

4. Quick Check:

   number pipe rounds decimals as per parameter [OK]

Hint: Number pipe rounds decimals between min and max digits [OK]

Common Mistakes:

• Ignoring thousand separators
• Not rounding decimals
• Confusing min and max decimal digits

4. What is wrong with this pipe usage?
{{ today | date:'yyyy-mm-dd' }}
Assuming today is a valid Date object.

medium

A. The pipe must be used with parentheses

B. The pipe name should be uppercase 'Date'

C. Date pipe does not accept format strings

D. The format string uses lowercase 'mm' which shows minutes, not months

Solution

1. Step 1: Check date format string

   In Angular date pipe, 'mm' means minutes, 'MM' means months.

2. Step 2: Identify the error

   Using 'yyyy-mm-dd' will show minutes instead of months, causing wrong output.

3. Final Answer:

   The format string uses lowercase 'mm' which shows minutes, not months -> Option D

4. Quick Check:

   Date pipe format is case-sensitive [OK]

Hint: Use uppercase MM for months in date pipe format [OK]

Common Mistakes:

• Using lowercase mm for months
• Capitalizing pipe names incorrectly
• Adding parentheses to pipes

5. You want to create a custom pipe truncate that shortens a string to a given length passed as a parameter. Which of these pipe transform method signatures correctly supports a parameter for length?

hard

A. transform(value: string, length: number): string

B. transform(value: string): string

C. transform(length: number, value: string): string

D. transform(): string

Solution

1. Step 1: Recall pipe transform method signature

   The first argument is the value, followed by optional parameters.

2. Step 2: Check parameter order and types

   transform(value: string, length: number): string correctly has value first, then length parameter.

3. Final Answer:

   transform(value: string, length: number): string -> Option A

4. Quick Check:

   Pipe transform(value, params...) signature [OK]

Hint: First argument is value, next are parameters in transform() [OK]

Common Mistakes:

• Swapping parameter order
• Omitting parameters
• Using no parameters at all