Parameterized pipes in Angular - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

Output of parameterized pipe with multiple parameters

Given the Angular pipe usage below, what will be the rendered output?

{{ 12345 | customFormat:'prefix':'suffix' }}

Assume the customFormat pipe adds the prefix and suffix strings around the number.

Angular

import { Pipe, PipeTransform } from '@angular/core';

@Pipe({name: 'customFormat'})
export class CustomFormatPipe implements PipeTransform {
  transform(value: number, prefix: string, suffix: string): string {
    return `${prefix}${value}${suffix}`;
  }
}

A 12345prefixsuffix

B 12345

C prefix 12345 suffix

D prefix12345suffix

💡 Hint

Remember the pipe parameters are passed in order after the value.

The pipe receives the value 12345 and parameters 'prefix' and 'suffix'. It returns the string with prefix + value + suffix concatenated without spaces.

📝 Syntax

intermediate

Correct syntax for passing multiple parameters to a pipe

Which of the following Angular template expressions correctly passes two parameters to a pipe named examplePipe?

A {{ value | examplePipe:param1:param2 }}

B {{ value | examplePipe:(param1, param2) }}

C {{ value | examplePipe[param1, param2] }}

D {{ value | examplePipe:param1;param2 }}

💡 Hint

Angular pipes accept parameters separated by colons.

Angular pipes accept multiple parameters separated by colons. Parentheses or brackets are not used for parameters in template expressions.

🔧 Debug

advanced

Why does this parameterized pipe produce unexpected output?

Consider this pipe code:

transform(value: string, prefix?: string, suffix?: string): string {
  return prefix + value + suffix;
}

When used as {{ 'test' | myPipe }}, it produces unexpected output ('undefinedtestundefined'). Why?

A The pipe transform method must always return a number, not string

B The pipe must have at least one parameter, so calling without parameters is invalid

C prefix and suffix are undefined, so concatenation includes the string 'undefined'

D Angular does not allow optional parameters in pipes

💡 Hint

Think about what happens when undefined is concatenated with strings.

When no parameters are passed, `prefix` and `suffix` are `undefined`. Concatenating `undefined` with strings in JavaScript results in the string 'undefined' being concatenated, producing 'undefinedtestundefined'. This leads to unexpected output.

❓ state_output

advanced

Output of pipe with parameter changing dynamically

In an Angular component template:

{{ value | repeat:times }}

where value = 'ha' and times is a component property starting at 2.

If times changes to 3, what is the new output?

Angular

import { Pipe, PipeTransform } from '@angular/core';

@Pipe({name: 'repeat'})
export class RepeatPipe implements PipeTransform {
  transform(value: string, times: number): string {
    return value.repeat(times);
  }
}

A haha

B hahaha

C ha3

D ha ha ha

💡 Hint

The repeat method repeats the string the given number of times without spaces.

When times is 3, value.repeat(3) returns 'hahaha' (ha repeated 3 times).

🧠 Conceptual

expert

Why use parameterized pipes instead of multiple pipes?

Which is the main advantage of using a parameterized pipe over chaining multiple pipes in Angular?

A It reduces template complexity by handling variations inside one pipe instead of multiple pipes

B Angular does not support chaining multiple pipes in templates

C Multiple pipes cannot accept parameters, only parameterized pipes can

D Parameterized pipes run faster because they are compiled differently

💡 Hint

Think about template readability and maintainability.

Parameterized pipes allow passing arguments to customize behavior inside one pipe, reducing the need to chain many pipes and making templates cleaner and easier to maintain.