Dynamic component loading in Angular - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is dynamic component loading in Angular?

Dynamic component loading means creating and inserting components into the app at runtime, not just when the app starts. It lets you add parts of the UI only when needed.

beginner

Which Angular service is commonly used to load components dynamically?

The ViewContainerRef service is used to create and insert components dynamically into the view.

intermediate

What is the role of ComponentFactoryResolver in dynamic component loading?

It helps create a factory for the component you want to load dynamically. This factory is then used to create the component instance.

intermediate

How do you clean up a dynamically loaded component in Angular?

You call the destroy() method on the component reference to remove it and free resources.

beginner

Why use dynamic component loading instead of static components?

It improves performance by loading components only when needed, and allows flexible UI changes without rebuilding the app.

Which Angular directive is used as a placeholder to insert a dynamic component?

A <ng-template>

B <div>

C <component>

D <router-outlet>

The directive acts as a placeholder where dynamic components can be inserted.

What method on ViewContainerRef inserts a component dynamically?

A insertComponent()

B appendChild()

C loadComponent()

D createComponent()

The createComponent() method creates and inserts a component dynamically into the container.

Which Angular version introduced the simplified dynamic component loading without ComponentFactoryResolver?

A Angular 9

B Angular 13

C Angular 14

D Angular 16

Angular 14 introduced a simpler API for dynamic component loading without needing ComponentFactoryResolver.

What is the type of object returned when you create a dynamic component?

A ComponentRef

B ElementRef

C ViewRef

D TemplateRef

Creating a dynamic component returns a ComponentRef, which represents the created component instance.

Which Angular feature helps to pass data to a dynamically loaded component?

A Router parameters

B Input properties

C Direct DOM manipulation

D Services only

Input properties can be set on the ComponentRef instance to pass data to the dynamic component.

Explain how to load a component dynamically in Angular step-by-step.

Think about the services and methods Angular provides for dynamic loading.

Describe benefits and use cases for dynamic component loading in Angular apps.

Consider why you might not want to load all components at once.

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