Web workers for heavy computation in Angular - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a web worker in Angular.

Angular

const worker = new Worker([1]);

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

A'./app.worker', { type: 'module' }

B'./app.worker.ts'

C'./app.worker.js'

D'./app.worker', { type: 'classic' }

Attempts:

3 left

💡 Hint

Common Mistakes

Including the file extension in the worker path.

Omitting the module type option.

Angular web workers are created by specifying the worker file path and the module type.

2fill in blank

medium

Complete the code to send a message to the web worker.

Angular

worker.[1]('start computation');

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

Aemit

Bsend

CpostMessage

Ddispatch

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent methods like send or emit.

Confusing with event dispatching.

Use postMessage to send data to a web worker.

3fill in blank

hard

Fix the error in the event listener to receive messages from the worker.

Angular

worker.addEventListener('[1]', ({ data }) => {
  console.log('Result:', data);
});

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

Aonmessage

BpostMessage

CmessageReceived

Dmessage

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'onmessage' as event name instead of 'message'.

Using non-standard event names.

The event name to listen for messages from a worker is message.

4fill in blank

hard

Fill both blanks to create a worker and send a message safely.

Angular

const worker = new Worker('[1]', { [2] });
worker.postMessage('compute');

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

A./heavy.worker

B./heavy.worker.js

Ctype: 'module'

Dtype: 'classic'

Attempts:

3 left

💡 Hint

Common Mistakes

Including file extensions in the path.

Using classic type instead of module.

Use the worker file path without extension and specify type: 'module' for Angular workers.

5fill in blank

hard

Fill all three blanks to create a worker, send a message, and listen for the result.

Angular

const worker = new Worker('[1]', { [2] });
worker.[3]('start');
worker.addEventListener('message', event => {
  console.log('Data:', event.data);
});

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

A./compute.worker

Btype: 'module'

CpostMessage

D./compute.worker.js

Attempts:

3 left

💡 Hint

Common Mistakes

Including '.js' in the worker path.

Using wrong method to send messages.

Use the worker path without extension, specify module type, and send messages with postMessage.

Practice

1. What is the main purpose of using Web Workers in an Angular application?

easy

A. To style components dynamically

B. To run heavy computations in the background without freezing the UI

C. To handle HTTP requests faster

D. To manage routing between pages

Solution

1. Step 1: Understand what Web Workers do

   Web Workers allow running scripts in background threads separate from the main UI thread.

2. Step 2: Identify the benefit in Angular apps

   This prevents the UI from freezing during heavy computations, improving user experience.

3. Final Answer:

   To run heavy computations in the background without freezing the UI -> Option B

4. Quick Check:

   Web Workers = background heavy tasks [OK]

Hint: Web Workers keep UI smooth by running heavy tasks separately [OK]

Common Mistakes:

• Thinking Web Workers handle UI styling
• Confusing Web Workers with HTTP request handlers
• Assuming Web Workers manage routing

2. Which Angular CLI command correctly creates a new Web Worker named compute?

easy

A. ng new worker compute

B. ng create worker compute

C. ng add worker compute

D. ng generate worker compute

Solution

1. Step 1: Recall Angular CLI syntax for generating workers

   The correct command to generate a worker is ng generate worker <name>.

2. Step 2: Match the command with the options

   Only ng generate worker compute uses the correct syntax: ng generate worker compute.

3. Final Answer:

   ng generate worker compute -> Option D

4. Quick Check:

   Generate worker = ng generate worker [OK]

Hint: Use 'ng generate worker' to create workers in Angular [OK]

Common Mistakes:

• Using 'ng create' instead of 'ng generate'
• Confusing 'ng add' with worker creation
• Trying 'ng new' which creates projects, not workers

3. Given this Angular Web Worker code snippet, what will be logged in the console?

const worker = new Worker(new URL('./compute.worker', import.meta.url));
worker.onmessage = ({ data }) => console.log('Result:', data);
worker.postMessage(10);

Assuming the worker script doubles the input number and sends it back.

medium

A. Result: undefined

B. Result: 10

C. Result: 20

D. Error: Worker not found

Solution

1. Step 1: Understand the message flow

   The main thread sends 10 to the worker using postMessage(10).

2. Step 2: Worker doubles the input and sends back

   The worker processes 10, doubles it to 20, and sends it back via postMessage.

3. Step 3: Main thread logs the received data

   The onmessage handler logs 'Result: 20'.

4. Final Answer:

   Result: 20 -> Option C

5. Quick Check:

   Input 10 doubled = 20 [OK]

Hint: Worker doubles input, so output is input x 2 [OK]

Common Mistakes:

• Assuming worker returns input unchanged
• Expecting undefined because of async timing
• Thinking worker script is missing causing error

4. What is the main error in this Angular Web Worker usage?

const worker = new Worker('./compute.worker');
worker.onmessage = (event) => console.log(event.data);
worker.postMessage(5);

medium

A. Missing import.meta.url in Worker URL

B. postMessage should be called before onmessage

C. Worker script path should be absolute URL

D. onmessage handler must be async function

Solution

1. Step 1: Check how the Worker is created

   In Angular, the worker URL must use new URL('./compute.worker', import.meta.url) for correct bundling.

2. Step 2: Identify the missing part

   The code uses a plain string './compute.worker' which causes a runtime error because the path is unresolved.

3. Final Answer:

   Missing import.meta.url in Worker URL -> Option A

4. Quick Check:

   Worker URL needs import.meta.url [OK]

Hint: Always use new URL(path, import.meta.url) for worker paths [OK]

Common Mistakes:

• Calling postMessage before setting onmessage
• Using absolute URL instead of relative with import.meta.url
• Making onmessage async unnecessarily

5. You want to perform a heavy calculation on a large array without freezing the UI. Which approach best uses Angular Web Workers to achieve this?

1. Create a worker with Angular CLI.
2. Send the large array to the worker using postMessage.
3. In the worker, process the array and send back the result.
4. Update the UI with the result when received.

What is the best practice to handle the large data transfer efficiently?

hard

A. Use Transferable Objects like ArrayBuffer to avoid copying data

B. Send data as JSON strings to simplify parsing

C. Split the array into small chunks and send each separately

D. Process the array on the main thread to avoid messaging overhead

Solution

1. Step 1: Understand data transfer in Web Workers

   Sending large data copies it by default, which can be slow and freeze UI.

2. Step 2: Use Transferable Objects to optimize

   Transferable Objects like ArrayBuffer transfer ownership without copying, making communication efficient.

3. Step 3: Compare options

   Sending JSON strings adds parsing overhead, splitting chunks adds complexity, and processing on main thread blocks UI.

4. Final Answer:

   Use Transferable Objects like ArrayBuffer to avoid copying data -> Option A

5. Quick Check:

   Transferable Objects = efficient large data transfer [OK]

Hint: Transfer large data with Transferable Objects to avoid UI freeze [OK]

Common Mistakes:

• Sending large data as JSON causing slow parsing
• Splitting data unnecessarily increasing complexity
• Processing heavy tasks on main thread causing freezes