Dynamic component loading in Angular - Performance & Optimization

Performance: Dynamic component loading

MEDIUM IMPACT

This affects the initial page load speed and interaction responsiveness by controlling when and how components are loaded and rendered.

Loading components that are not immediately visible on the page

Angular

import { ViewContainerRef, Component } from '@angular/core';

@Component({
  selector: 'app-root',
  template: `<ng-template #container></ng-template>`
})
export class AppComponent {
  constructor(private vcr: ViewContainerRef) {}

  async loadComponent() {
    const { ComponentA } = await import('./component-a');
    this.vcr.clear();
    this.vcr.createComponent(ComponentA);
  }
}

ComponentA is loaded only when loadComponent() is called, reducing initial bundle size and speeding up first paint.

📈 Performance GainSaves tens of KBs on initial load, reduces blocking time, improves LCP

Loading components that are not immediately visible on the page

Angular

import { ComponentA } from './component-a';

@Component({
  selector: 'app-root',
  template: `<component-a></component-a>`
})
export class AppComponent {}

ComponentA is loaded and rendered immediately, increasing initial bundle size and delaying page load.

📉 Performance CostIncreases bundle size by tens of KBs, blocks rendering until component loads

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Static import and render	High (all components created at start)	Multiple (due to many components)	High (all painted immediately)	[X] Bad
Dynamic import with lazy loading	Low (only loaded components created)	Single or few (on-demand)	Low (only painted when needed)	[OK] Good

Rendering Pipeline

Dynamic component loading delays the creation and rendering of components until explicitly requested, reducing initial style calculation and layout work.

→Script Parsing

→Style Calculation

→Layout

→Paint

⚠️ BottleneckScript Parsing and Layout during initial load

Core Web Vital Affected

LCP, INP

This affects the initial page load speed and interaction responsiveness by controlling when and how components are loaded and rendered.

Optimization Tips

1Use dynamic imports to load components only when needed.

2Avoid loading all components upfront to reduce initial bundle size.

3Balance lazy loading to prevent interaction delays.

Performance Quiz - 3 Questions

What is the main performance benefit of dynamic component loading in Angular?

A Blocks rendering until all components are loaded

B Increases the number of DOM nodes on page load

C Reduces initial bundle size and speeds up first paint

D Automatically caches all components in memory

DevTools: Performance

How to check: Record a performance profile during page load and interaction. Look for script parsing and layout times related to component creation.

What to look for: Long scripting and layout blocks during initial load indicate static loading; shorter initial blocks with deferred component creation indicate good dynamic loading.

Practice

1. What is the main purpose of dynamic component loading in Angular?

easy

A. To add components to the view while the app is running

B. To statically declare all components in the template

C. To improve CSS styling of components

D. To replace Angular modules with components

Solution

1. Step 1: Understand dynamic component loading

   Dynamic component loading means adding components to the app view during runtime, not just at compile time.

2. Step 2: Compare options

   Only To add components to the view while the app is running describes adding components while the app runs. Other options describe static or unrelated concepts.

3. Final Answer:

   To add components to the view while the app is running -> Option A

4. Quick Check:

   Dynamic loading = add components at runtime [OK]

Hint: Dynamic loading means adding components during app run [OK]

Common Mistakes:

• Confusing dynamic loading with static template declaration
• Thinking it changes CSS or modules
• Assuming it replaces Angular modules

2. Which Angular service is used to insert a dynamic component into the view?

easy

A. Renderer2

B. HttpClient

C. ViewContainerRef

D. NgModuleRef

Solution

1. Step 1: Identify the service for dynamic insertion

   ViewContainerRef provides a container where components can be dynamically added or removed.

2. Step 2: Eliminate other options

   Renderer2 is for DOM manipulation, HttpClient for HTTP calls, NgModuleRef for module references, none for dynamic component insertion.

3. Final Answer:

   ViewContainerRef -> Option C

4. Quick Check:

   Dynamic insertion uses ViewContainerRef [OK]

Hint: Use ViewContainerRef to insert dynamic components [OK]

Common Mistakes:

• Choosing Renderer2 which is for DOM, not components
• Confusing HttpClient with component loading
• Using NgModuleRef incorrectly

3. Given this code snippet, what will be the output in the browser?

const componentRef = viewContainerRef.createComponent(MyComponent);
componentRef.instance.title = 'Hello';

Assuming MyComponent displays {{ title }} in its template.

medium

A. The component will load but title will be empty

B. The text 'Hello' will appear where the component is loaded

C. Nothing will appear because the component is not attached

D. An error because title is not a valid property

Solution

1. Step 1: Understand createComponent and instance property

   createComponent adds the component to the view. Setting instance.title assigns the property used in the template.

2. Step 2: Predict rendered output

   Since {{ title }} is displayed, and title is set to 'Hello', the text 'Hello' will appear.

3. Final Answer:

   The text 'Hello' will appear where the component is loaded -> Option B

4. Quick Check:

   Set instance property = visible text [OK]

Hint: Setting instance properties updates displayed content [OK]

Common Mistakes:

• Thinking component is not attached after createComponent
• Assuming property must be declared differently
• Ignoring that instance properties affect template

4. What is wrong with this code snippet for dynamic component loading?

@ViewChild('container', { read: ViewContainerRef }) containerRef!: ViewContainerRef;

load() {
  const comp = this.containerRef.createComponent(SomeComponent);
  comp.instance.data = 'Test';
}

medium

A. ViewChild should not use read option

B. Using createComponent without importing ComponentFactoryResolver

C. Cannot assign data property on instance

D. Missing #container template reference in HTML

Solution

1. Step 1: Check ViewChild usage

   ViewChild with #container expects a matching template reference variable in HTML.

2. Step 2: Identify missing template reference

   If #container is missing in the template, containerRef will be undefined, causing runtime errors.

3. Final Answer:

   Missing #container template reference in HTML -> Option D

4. Quick Check:

   ViewChild needs matching template ref [OK]

Hint: Always add matching #ref in template for ViewChild [OK]

Common Mistakes:

• Assuming ComponentFactoryResolver is needed in Angular 14+
• Thinking instance properties can't be assigned
• Misusing read option in ViewChild

5. You want to load different components dynamically based on user input. Which approach correctly handles this scenario in Angular?

hard

A. Use a single ViewContainerRef and call createComponent() with the chosen component type each time, clearing previous components

B. Declare all possible components in the template and use *ngIf to show/hide them

C. Create components manually with new keyword and append to DOM

D. Use Angular modules to switch components dynamically without ViewContainerRef

Solution

1. Step 1: Understand dynamic component switching

   Using ViewContainerRef with createComponent allows loading different components at runtime by clearing old ones and adding new.

2. Step 2: Evaluate other options

   Declare all possible components in the template and use *ngIf to show/hide them is static and less flexible. Create components manually with new keyword and append to DOM bypasses Angular and breaks framework rules. Use Angular modules to switch components dynamically without ViewContainerRef misunderstands modules' role.

3. Final Answer:

   Use a single ViewContainerRef and call createComponent() with the chosen component type each time, clearing previous components -> Option A

4. Quick Check:

   Dynamic switching = clear + createComponent [OK]

Hint: Clear container then create chosen component dynamically [OK]

Common Mistakes:

• Using static *ngIf instead of dynamic loading
• Trying to create components with new keyword
• Confusing modules with dynamic component loading