(Answer from ChatGPT:)
In Angular 18, signals, computed, and effects are reactive primitives designed to handle state and trigger updates in a precise and efficient way. Here’s an overview of these concepts and guidance on when to use them:
1. Signals
What are they? • Signals are containers for reactive state. They hold a value and notify consumers when the value changes. • They are functions that can: • Get the current value by calling the function (e.g., signal()). • Set a new value using .set(). • Update the value based on the current one using .update().
Example:
import { signal } from ‘@angular/core’;
const counter = signal(0);
counter.set(5); // Update the value to 5 console.log(counter()); // Access the value: 5 counter.update(value => value + 1); // Increment value: 6
When to use: • Use signals for local, standalone state management, like managing counters, toggles, or other simple values that change over time. • Ideal when you want fine-grained reactivity without affecting the entire component tree.
2. Computed
What are they? • Computed signals derive their value from other signals. They automatically recalculate whenever the underlying signals change. • Think of them as “read-only reactive values.”
Example:
import { signal, computed } from ‘@angular/core’;
const firstName = signal(‘John’); const lastName = signal(‘Doe’);
const fullName = computed(() => `${firstName()} ${lastName()}`); console.log(fullName()); // “John Doe”
firstName.set(‘Jane’); console.log(fullName()); // Automatically updates: “Jane Doe”
When to use: • Use computed signals when you need to derive or transform data from other signals. • Common for calculated values or formatting outputs based on state changes.
3. Effects
What are they? • Effects are side-effect mechanisms that execute whenever a signal or computed signal they depend on changes. • They’re useful for triggering actions like API calls, DOM updates, or logging when reactive state changes.
Example:
import { signal, effect } from ‘@angular/core’;
const count = signal(0);
effect(() => { console.log(`Count changed to: ${count()}`); });
count.set(1); // Logs: “Count changed to: 1”
When to use: • Use effects for performing side effects tied to reactive state changes. • Examples include: • Triggering HTTP requests. • Updating a non-reactive DOM element. • Debugging or logging.
How to Decide Which to Use
Use Case Preferred Concept Storing a piece of state Signal Calculating derived state Computed Performing side effects (e.g., API calls, logging) Effect
Best Practices 1. Minimize Effects: Use effects sparingly for true side effects only. Avoid embedding complex logic within effects—prefer signals and computed signals for managing data. 2. Avoid Nested Computed/Effects: Keep the dependency graph clear to maintain predictability and avoid performance bottlenecks. 3. Compose Signals and Computed: Combine these primitives for a clean, reactive data flow.
By choosing the right concept for your needs, you can create Angular applications that are more efficient, readable, and maintainable【8】【9】【10】.
In Angular 18, signals, computed, and effects are reactive primitives designed to handle state and trigger updates in a precise and efficient way. Here’s an overview of these concepts and guidance on when to use them:
1. Signals
What are they? • Signals are containers for reactive state. They hold a value and notify consumers when the value changes. • They are functions that can: • Get the current value by calling the function (e.g., signal()). • Set a new value using .set(). • Update the value based on the current one using .update().
Example:
import { signal } from ‘@angular/core’;
const counter = signal(0);
counter.set(5); // Update the value to 5 console.log(counter()); // Access the value: 5 counter.update(value => value + 1); // Increment value: 6
When to use: • Use signals for local, standalone state management, like managing counters, toggles, or other simple values that change over time. • Ideal when you want fine-grained reactivity without affecting the entire component tree.
2. Computed
What are they? • Computed signals derive their value from other signals. They automatically recalculate whenever the underlying signals change. • Think of them as “read-only reactive values.”
Example:
import { signal, computed } from ‘@angular/core’;
const firstName = signal(‘John’); const lastName = signal(‘Doe’);
const fullName = computed(() => `${firstName()} ${lastName()}`); console.log(fullName()); // “John Doe”
firstName.set(‘Jane’); console.log(fullName()); // Automatically updates: “Jane Doe”
When to use: • Use computed signals when you need to derive or transform data from other signals. • Common for calculated values or formatting outputs based on state changes.
3. Effects
What are they? • Effects are side-effect mechanisms that execute whenever a signal or computed signal they depend on changes. • They’re useful for triggering actions like API calls, DOM updates, or logging when reactive state changes.
Example:
import { signal, effect } from ‘@angular/core’;
const count = signal(0);
effect(() => { console.log(`Count changed to: ${count()}`); });
count.set(1); // Logs: “Count changed to: 1”
When to use: • Use effects for performing side effects tied to reactive state changes. • Examples include: • Triggering HTTP requests. • Updating a non-reactive DOM element. • Debugging or logging.
How to Decide Which to Use
Use Case Preferred Concept Storing a piece of state Signal Calculating derived state Computed Performing side effects (e.g., API calls, logging) Effect
Best Practices 1. Minimize Effects: Use effects sparingly for true side effects only. Avoid embedding complex logic within effects—prefer signals and computed signals for managing data. 2. Avoid Nested Computed/Effects: Keep the dependency graph clear to maintain predictability and avoid performance bottlenecks. 3. Compose Signals and Computed: Combine these primitives for a clean, reactive data flow.
By choosing the right concept for your needs, you can create Angular applications that are more efficient, readable, and maintainable【8】【9】【10】.
