Shared modules for reusable components in Angular - Mini Project: Build & Apply

Shared modules for reusable components

📖 Scenario: You are building an Angular app with multiple pages. You want to reuse a button component across these pages without rewriting it each time.

🎯 Goal: Create a shared Angular module that contains a reusable button component. Then import this shared module into another component to use the button.

📋 What You'll Learn

Create a standalone button component with a template showing a button with text 'Click me'

Create a shared Angular module named SharedModule that declares and exports the button component

Import SharedModule into a new standalone component named HomeComponent

Use the button component selector inside HomeComponent's template

💡 Why This Matters

🌍 Real World

Shared modules help organize reusable UI parts like buttons, cards, or forms in large Angular apps, making code easier to maintain and reuse.

💼 Career

Understanding shared modules and reusable components is essential for Angular developers working on scalable, maintainable enterprise applications.

1

Create a standalone button component

Create a standalone Angular component named ButtonComponent with selector app-button. Its template should contain a <button> element with the text Click me. Use the @Component decorator with standalone: true.

Angular

# Your code here to create ButtonComponent as a standalone component with selector 'app-button' and template 'Click me'

Hint

Use @Component with standalone: true and define the selector and template exactly as instructed.

2

Create a shared module exporting the button component

Create an Angular module named SharedModule using @NgModule. It should declare and export ButtonComponent. Import ButtonComponent in this module file. The module should NOT be standalone.

Angular

import { NgModule } from '@angular/core';
// Your code here to create SharedModule that declares and exports ButtonComponent

Hint

Use @NgModule with declarations and exports arrays including ButtonComponent.

3

Create a standalone HomeComponent importing SharedModule

Create a standalone Angular component named HomeComponent with selector app-home. Import SharedModule in its imports array. The template should contain the <app-button> element to use the button component.

Angular

import { Component } from '@angular/core';
import { SharedModule } from './shared.module';

// Your code here to create HomeComponent as standalone with selector 'app-home', import SharedModule, and template using 

Hint

Use @Component with standalone: true, import SharedModule, and include <app-button> in the template.

4

Use HomeComponent in your app

Add <app-home> to your main app component template or bootstrap HomeComponent in your Angular app to display the reusable button.

Angular

// Your code here to add  in main app template or bootstrap HomeComponent

Hint

Use bootstrapApplication(HomeComponent) to start the app with HomeComponent showing the reusable button.

Practice

1. What is the main purpose of a shared module in Angular?

easy

A. To store environment configuration settings

B. To define the root component of the application

C. To group reusable components, directives, and pipes for easy sharing

D. To handle routing between different pages

Solution

1. Step 1: Understand the role of shared modules

   Shared modules are designed to hold components, directives, and pipes that multiple parts of the app can use.

2. Step 2: Compare with other module purposes

   Root modules handle app startup, routing modules manage navigation, and environment files store settings, not reusable UI parts.

3. Final Answer:

   To group reusable components, directives, and pipes for easy sharing -> Option C

4. Quick Check:

   Shared module = reusable parts [OK]

Hint: Shared modules bundle reusable UI parts for easy import [OK]

Common Mistakes:

• Confusing shared modules with root or routing modules
• Thinking shared modules store app settings
• Assuming shared modules handle navigation

2. Which of the following is the correct way to export a component from a shared module?

easy

A. Add the component to both declarations and exports arrays in @NgModule

B. Add the component only to the imports array

C. Add the component only to the providers array

D. Add the component only to the bootstrap array

Solution

1. Step 1: Understand Angular module metadata

   Components must be declared in declarations to be recognized, and exported in exports to be usable outside the module.

2. Step 2: Check other arrays usage

   Imports bring in other modules, providers register services, bootstrap is for root components only.

3. Final Answer:

   Add the component to both declarations and exports arrays in @NgModule -> Option A

4. Quick Check:

   Declare + export = share component [OK]

Hint: Declare and export components to share them outside module [OK]

Common Mistakes:

• Putting components only in imports or providers
• Forgetting to export after declaring
• Using bootstrap array in shared modules

3. Given this shared module code, what will be the output when FeatureComponent uses SharedButtonComponent?

@NgModule({
  declarations: [SharedButtonComponent],
  exports: [SharedButtonComponent]
})
export class SharedModule {}

@NgModule({
  imports: [SharedModule],
  declarations: [FeatureComponent]
})
export class FeatureModule {}

If FeatureComponent template contains <app-shared-button>Click</app-shared-button>, what happens?

medium

A. The button renders correctly with text 'Click'

B. Error: 'app-shared-button' is not a known element

C. The button renders but without text

D. The app crashes at runtime

Solution

1. Step 1: Check module imports and exports

   SharedButtonComponent is declared and exported in SharedModule, which is imported by FeatureModule.

2. Step 2: Confirm component usage in FeatureComponent

   Since FeatureModule imports SharedModule, FeatureComponent can use SharedButtonComponent selector without error.

3. Final Answer:

   The button renders correctly with text 'Click' -> Option A

4. Quick Check:

   Imported shared module exports = component usable [OK]

Hint: Import shared module to use its exported components [OK]

Common Mistakes:

• Not importing SharedModule in FeatureModule
• Forgetting to export component in SharedModule
• Using component selector incorrectly

4. Identify the error in this shared module setup:

@NgModule({
  declarations: [SharedCardComponent],
  imports: [CommonModule]
})
export class SharedModule {}

@NgModule({
  imports: [SharedModule],
  declarations: [DashboardComponent]
})
export class DashboardModule {}

DashboardComponent template uses <app-shared-card> but Angular throws an error.

medium

A. CommonModule should not be imported in SharedModule

B. DashboardComponent should import SharedCardComponent directly

C. DashboardModule should declare SharedCardComponent again

D. SharedCardComponent is not exported from SharedModule

Solution

1. Step 1: Check SharedModule exports

   SharedCardComponent is declared but not exported, so other modules can't use it.

2. Step 2: Understand Angular module sharing rules

   To use a component from another module, it must be exported by that module.

3. Final Answer:

   SharedCardComponent is not exported from SharedModule -> Option D

4. Quick Check:

   Declare + export needed to share component [OK]

Hint: Always export components to share them outside module [OK]

Common Mistakes:

• Forgetting to export declared components
• Trying to redeclare components in feature modules
• Misunderstanding imports vs exports

5. You want to create a shared module that provides a reusable button component and a custom pipe. Which setup correctly allows any feature module to use both without redeclaring them?

// SharedModule
@NgModule({
  declarations: [SharedButtonComponent, CustomPipe],
  exports: [SharedButtonComponent, CustomPipe],
  imports: [CommonModule]
})
export class SharedModule {}

// FeatureModule
@NgModule({
  imports: [SharedModule],
  declarations: [FeatureComponent]
})
export class FeatureModule {}

What must you do in FeatureComponent template to use both?

hard

A. Import SharedButtonComponent and CustomPipe directly in FeatureComponent

B. Use <app-shared-button> and apply | customPipe in template expressions

C. Declare SharedButtonComponent and CustomPipe again in FeatureModule

D. Use <shared-button> and | CustomPipe with capital letters

Solution

1. Step 1: Confirm shared module exports

   SharedButtonComponent and CustomPipe are declared and exported in SharedModule, which FeatureModule imports.

2. Step 2: Use correct selectors and pipe names

   FeatureComponent can use selector and apply | customPipe (pipe names are case-sensitive and lowercase by convention).

3. Final Answer:

   Use <app-shared-button> and apply | customPipe in template expressions -> Option B

4. Quick Check:

   Import shared module + use selectors and pipe names correctly [OK]

Hint: Use exported selectors and pipe names exactly as declared [OK]

Common Mistakes:

• Redeclaring shared components or pipes in feature modules
• Using wrong selector or pipe name casing
• Trying to import components or pipes directly