pipe method for chaining operators in Angular - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a signal that doubles its value using the pipe method.

Angular

const doubled = signal(5).[1](map(x => x * 2));

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

Apipe

Bsubscribe

Cmap

Dfilter

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'subscribe' instead of 'pipe' which is for observables, not signals.

Trying to call 'map' directly on the signal without 'pipe'.

The pipe method is used to chain operators like map on signals in Angular.

2fill in blank

medium

Complete the code to chain two operators: map and filter using the pipe method.

Angular

const result = signal(10).[1](map(x => x + 5), filter(x => x > 10));

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

AswitchMap

Bpipe

Ctap

Dsubscribe

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'subscribe' which is for consuming observables, not chaining operators.

Trying to call operators without using 'pipe'.

The pipe method chains multiple operators like map and filter on a signal.

3fill in blank

hard

Fix the error in the code by completing the method to chain operators correctly.

Angular

const updated = signal(3).[1](filter(x => x > 1), map(x => x * 10));

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

Apipe

Bsubscribe

Cmap

Dfilter

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'subscribe' which is for observables, not signals.

Calling 'map' or 'filter' directly without 'pipe'.

The pipe method is required to chain multiple operators like filter and map on a signal.

4fill in blank

hard

Fill both blanks to create a signal that filters values greater than 5 and then maps them to their squares.

Angular

const processed = signal([2, 6, 8]).[1](filter(x => x > 5), [2](x => x * x));

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

Apipe

Bmap

Cfilter

Dsubscribe

Attempts:

3 left

💡 Hint

Common Mistakes

Putting 'subscribe' instead of 'pipe' for chaining.

Swapping 'filter' and 'map' in the wrong places.

Use pipe to chain operators, first filter then map to transform the signal values.

5fill in blank

hard

Fill all three blanks to chain operators that filter even numbers, map them to strings, and then tap to log each value.

Angular

const final = signal([1, 2, 3, 4]).[1](filter(x => x % 2 === 0), [2](x => x.toString()), [3](x => console.log(x)));

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

Apipe

Bmap

Ctap

Dsubscribe

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'subscribe' instead of 'pipe' for chaining.

Mixing up 'tap' and 'map' operators.

Use pipe to chain filter, map, and tap operators on the signal.

Practice

1. What is the main purpose of the pipe method in Angular when working with Observables?

easy

A. To create a new Observable from scratch

B. To subscribe to the Observable and start data flow

C. To chain multiple operators for transforming data streams

D. To convert an Observable into a Promise

Solution

1. Step 1: Understand the role of pipe

   The pipe method is used to chain operators that transform or filter data in an Observable stream.

2. Step 2: Differentiate from subscription

   Subscribing starts the data flow, but pipe only sets up the chain of operations.

3. Final Answer:

   To chain multiple operators for transforming data streams -> Option C

4. Quick Check:

   pipe chains operators = C [OK]

Hint: Remember: pipe chains, subscribe starts flow [OK]

Common Mistakes:

• Confusing pipe with subscribe
• Thinking pipe creates Observables
• Assuming pipe converts to Promise

2. Which of the following is the correct syntax to chain two operators map and filter using the pipe method on an Observable named obs$?

easy

A. obs$.pipe(map(x => x * 2), filter(x => x > 5))

B. obs$.pipe(map(x => x * 2).filter(x => x > 5))

C. obs$.map(x => x * 2).pipe(filter(x => x > 5))

D. obs$.filter(x => x > 5).pipe(map(x => x * 2))

Solution

1. Step 1: Recall correct pipe syntax

   The pipe method takes operators as arguments separated by commas inside parentheses.

2. Step 2: Check chaining order and method calls

   Only pipe is called once with both operators inside; chaining operators outside pipe is incorrect.

3. Final Answer:

   obs$.pipe(map(x => x * 2), filter(x => x > 5)) -> Option A

4. Quick Check:

   pipe(args separated by commas) = D [OK]

Hint: Use one pipe with comma-separated operators [OK]

Common Mistakes:

• Calling pipe multiple times incorrectly
• Chaining operators outside pipe
• Using dot notation on operators

3. Given the following code, what will be the output logged to the console?

import { of } from 'rxjs';
import { map, filter } from 'rxjs/operators';

const obs$ = of(1, 2, 3, 4, 5);
obs$.pipe(
  filter(x => x % 2 === 1),
  map(x => x * 10)
).subscribe(console.log);

medium

A. 1, 3, 5

B. 10, 30, 50

C. 2, 4

D. 20, 40

Solution

1. Step 1: Apply filter operator

   The filter keeps only odd numbers: 1, 3, 5.

2. Step 2: Apply map operator

   Each filtered value is multiplied by 10: 10, 30, 50.

3. Final Answer:

   10, 30, 50 -> Option B

4. Quick Check:

   filter odds then multiply by 10 = A [OK]

Hint: Filter first, then map inside pipe [OK]

Common Mistakes:

• Mixing order of operators
• Forgetting to subscribe
• Assuming filter keeps even numbers

4. Identify the error in the following code snippet that uses the pipe method:

import { of } from 'rxjs';
import { map, filter } from 'rxjs/operators';

const obs$ = of(1, 2, 3);
obs$.pipe(
  map(x => x * 2),
  filter(x => x > 3)
).subscribe(console.log());

medium

A. Calling subscribe with parentheses executes immediately

B. Incorrect import of operators

C. Missing semicolon after pipe method

D. Using arrow functions inside pipe is invalid

Solution

1. Step 1: Check subscribe usage

   The code calls subscribe(console.log()) which immediately executes console.log and passes its result (undefined) to subscribe.

2. Step 2: Correct subscribe usage

   It should be subscribe(console.log) without parentheses to pass the function reference.

3. Final Answer:

   Calling subscribe with parentheses executes immediately -> Option A

4. Quick Check:

   subscribe needs function reference, not call = A [OK]

Hint: Pass function to subscribe, don't call it [OK]

Common Mistakes:

• Calling subscribe with parentheses
• Confusing operator imports
• Thinking semicolon affects pipe chaining

5. You want to create an Observable pipeline that takes numbers, filters out falsy values (like 0), doubles the remaining numbers, and then converts them to strings with a prefix 'Value: '. Which of the following pipe chains correctly achieves this?

hard

A. obs$.pipe(map(x => `Value: ${x * 2}`), filter(x => !!x))

B. obs$.pipe(map(x => x * 2), filter(x => x), map(x => `Value: ${x}`))

C. obs$.pipe(filter(x => x !== 0), map(x => x * 2), map(x => `Value: ${x}`))

D. obs$.pipe(filter(x => !!x), map(x => `Value: ${x * 2}`))

Solution

1. Step 1: Filter out falsy values

   Using filter(x => !!x) removes falsy values like 0, null, undefined.

2. Step 2: Map to doubled string with prefix

   The map operator transforms the number by doubling and adding the prefix string.

3. Final Answer:

   obs$.pipe(filter(x => !!x), map(x => `Value: ${x * 2}`)) -> Option D

4. Quick Check:

   Filter falsy then map to string = B [OK]

Hint: Filter falsy first, then map to string [OK]

Common Mistakes:

• Mapping before filtering falsy values
• Using multiple maps unnecessarily
• Filtering after mapping to string