Why signals are introduced in Angular - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a signal in Angular.

Angular

const count = [1](0);

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

Asignal

BuseState

Cref

Dreactive

Attempts:

3 left

💡 Hint

Common Mistakes

Using React hooks like useState instead of Angular signals.

Using ref which is from Vue, not Angular.

In Angular, signal is used to create reactive state that updates the UI automatically.

2fill in blank

medium

Complete the code to update a signal's value.

Angular

count.[1]((prev) => prev + 1);

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

Aset

Bupdate

Cnext

Dchange

Attempts:

3 left

💡 Hint

Common Mistakes

Using set which replaces the value directly, not updates it.

Using non-existent methods like next or change.

The update method changes the signal's value based on the current value.

3fill in blank

hard

Fix the error in the code to read a signal's value.

Angular

const current = count[1];

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

A.get()

B.value

C[]

D()

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to access a property like .value which does not exist.

Using square brackets which are invalid here.

Signals are functions, so to get their value you call them with ().

4fill in blank

hard

Fill both blanks to create a computed signal that doubles the count.

Angular

const doubleCount = [1](() => count() [2] 2);

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

Acomputed

B*

C+

Dsignal

Attempts:

3 left

💡 Hint

Common Mistakes

Using signal instead of computed for derived values.

Using addition + instead of multiplication.

computed creates a signal derived from others. Multiplying count by 2 doubles it.

5fill in blank

hard

Fill all three blanks to create a signal, update it, and read its value.

Angular

const score = [1](10);
score.[2](prev => prev [3] 5);

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

Asignal

Bupdate

C+

Dcomputed

Attempts:

3 left

💡 Hint

Common Mistakes

Using computed to create the initial signal.

Using set instead of update when a function is passed.

Using subtraction - instead of addition.

Create a signal with signal, update it with update, and add 5 using +.

Practice

1. Why were signals introduced in Angular?

easy

A. To make it easier to track and react to data changes

B. To replace all Angular directives

C. To remove the need for components

D. To simplify CSS styling

Solution

1. Step 1: Understand the purpose of signals

   Signals help Angular track changes in data and update the UI efficiently.

2. Step 2: Compare with other options

   Replacing directives, removing components, or simplifying CSS are unrelated to signals.

3. Final Answer:

   To make it easier to track and react to data changes -> Option A

4. Quick Check:

   Signals improve data tracking = C [OK]

Hint: Signals help track data changes easily [OK]

Common Mistakes:

• Thinking signals replace Angular directives
• Confusing signals with styling tools
• Believing signals remove components

2. Which of the following is the correct way to create a signal in Angular?

easy

A. const count = createSignal(0);

B. const count = new Signal(0);

C. const count = signal(0);

D. const count = signal.create(0);

Solution

1. Step 1: Recall Angular signal syntax

   The correct syntax uses the function signal() to create a signal.

2. Step 2: Check other options

   Options B, C, and D use incorrect constructors or methods not in Angular's signal API.

3. Final Answer:

   const count = signal(0); -> Option C

4. Quick Check:

   Use signal() function to create signals = A [OK]

Hint: Use signal() function to create signals [OK]

Common Mistakes:

• Using new keyword with Signal
• Calling createSignal instead of signal
• Using dot notation like signal.create

3. Given this Angular code snippet:

const count = signal(0);
count.set(5);
console.log(count());

What will be printed in the console?

medium

A. 5

B. undefined

C. signal(0)

D. 0

Solution

1. Step 1: Understand signal creation and update

   The signal count starts at 0, then count.set(5) updates its value to 5.

2. Step 2: Evaluate the console.log output

   Calling count() returns the current value, which is 5 after the update.

3. Final Answer:

   5 -> Option A

4. Quick Check:

   Signal value after set(5) = 5 [OK]

Hint: Calling signal() returns current value [OK]

Common Mistakes:

• Thinking count() returns the initial value
• Confusing signal object with its value
• Expecting undefined without set call

4. What is wrong with this Angular signal code?

const count = signal(0);
count = signal(5);

medium

A. signal() cannot hold numbers

B. signal() must be called with a string

C. count() should be used instead of count

D. Signals cannot be reassigned like this

Solution

1. Step 1: Understand signal immutability

   Signals are constants; you cannot reassign the variable holding a signal.

2. Step 2: Check other options

   signal() accepts numbers, and count() is for reading value, not reassignment.

3. Final Answer:

   Signals cannot be reassigned like this -> Option D

4. Quick Check:

   Signal variables are constant references = A [OK]

Hint: Signals are constants; don't reassign them [OK]

Common Mistakes:

• Trying to reassign signal variables
• Confusing signal creation with value reading
• Thinking signal only accepts strings

5. How do signals improve Angular app performance compared to traditional change detection?

hard

A. By running change detection on the entire app every time

B. By updating only the parts of the UI that depend on changed data

C. By disabling all UI updates until manual refresh

D. By removing the need for templates

Solution

1. Step 1: Understand traditional change detection

   Traditional Angular runs change detection on many components, which can be slow.

2. Step 2: Understand signals' selective update

   Signals update only UI parts that depend on changed data, improving speed and efficiency.

3. Step 3: Evaluate options

   By updating only the parts of the UI that depend on changed data correctly describes signals' selective update. By disabling all UI updates until manual refresh is incorrect because signals do not disable UI updates.

4. Final Answer:

   By updating only the parts of the UI that depend on changed data -> Option B

5. Quick Check:

   Signals update only needed UI parts = B [OK]

Hint: Signals update only affected UI parts [OK]

Common Mistakes:

• Thinking signals disable UI updates
• Believing change detection runs everywhere always
• Assuming signals remove templates