Unveiling the Mystery of Angular: Why are constructor parameters without access specifiers hidden from view outside the

Question

Unveiling the Mystery of Angular: Why are constructor parameters without access specifiers hidden from view outside the

When I explicitly set an access specifier for a constructor parameter, it becomes visible outside the constructor. For example:

constructor(private employeResourceService:EmployeeResourceService ){
//code}
 ngOnInit(){
    this.employeResourceService=undefined;//possible

  }

However, when I remove the access specifier, constructor parameters are not visible outside the constructor. For example:

 constructor(employeResourceService:EmployeeResourceService ){
    //code}
     ngOnInit(){
        this.employeResourceService=undefined;//not visible

      }

Why does this happen? Does TypeScript lack a default access specifier like Java?

angular typescript

Answer 1

Answer №1

Providing an access specifier to a function parameter may seem unnecessary. However, in TypeScript, you have the ability to do so when defining a constructor. The purpose of this is as follows: when you declare

class MyClass {
  constructor(private employeResourceService: EmployeeResourceService){
    //code
  }
}

this code is essentially a shorthand for

class MyClass {
  private employeResourceService: EmployeeResourceService
  constructor(employeResourceService: EmployeeResourceService){
    this.employeResourceService = employeResourceService
    //code
  }
}

Therefore, with one line of code, you not only define an instance parameter but also assign it the value passed as a parameter. This shortcut only applies if you provide an access specifier. Without it, the parameter simply functions as a regular function parameter without being declared as an instance parameter or assigned any value.

Furthermore, there exists a default access value, but to utilize it, you must manually declare the instance parameter and assign its value:

class MyClass {
  employeResourceService: EmployeeResourceService
  constructor(employeResourceService: EmployeeResourceService){
    this.employeResourceService = employeResourceService
    //code
  }
}

Answer 2

Providing an access specifier to a function parameter may seem unnecessary. However, in TypeScript, you have the ability to do so when defining a constructor. The purpose of this is as follows: when you declare

class MyClass {
  constructor(private employeResourceService: EmployeeResourceService){
    //code
  }
}

this code is essentially a shorthand for

class MyClass {
  private employeResourceService: EmployeeResourceService
  constructor(employeResourceService: EmployeeResourceService){
    this.employeResourceService = employeResourceService
    //code
  }
}

Therefore, with one line of code, you not only define an instance parameter but also assign it the value passed as a parameter. This shortcut only applies if you provide an access specifier. Without it, the parameter simply functions as a regular function parameter without being declared as an instance parameter or assigned any value.

Furthermore, there exists a default access value, but to utilize it, you must manually declare the instance parameter and assign its value:

class MyClass {
  employeResourceService: EmployeeResourceService
  constructor(employeResourceService: EmployeeResourceService){
    this.employeResourceService = employeResourceService
    //code
  }
}

Answer 3

Answer №2

The purpose behind this approach is to streamline the code: by adding an access modifier to the input parameter in the constructor, you are essentially declaring and assigning a field within the class in a more concise manner.

This practice is well-documented at https://www.typescriptlang.org/docs/handbook/classes.html#parameter-properties

Additionally, it's worth noting that Typescript does offer a default mode for input parameters when they are only needed in the constructor and not thereafter. A prime example of this is the FormBuilder, which is typically used once without the need to store it in a separate field.

Answer 4

The purpose behind this approach is to streamline the code: by adding an access modifier to the input parameter in the constructor, you are essentially declaring and assigning a field within the class in a more concise manner.

This practice is well-documented at https://www.typescriptlang.org/docs/handbook/classes.html#parameter-properties

Additionally, it's worth noting that Typescript does offer a default mode for input parameters when they are only needed in the constructor and not thereafter. A prime example of this is the FormBuilder, which is typically used once without the need to store it in a separate field.

Unveiling the Mystery of Angular: Why are constructor parameters without access specifiers hidden from view outside the

Answer №1

Answer №2

Similar questions

Creating an HTML tag from Angular using TypeScript

There are currently no examples demonstrating how to populate row headers and dynamic columns in the Material table

Consecutive API requests within React context

Importing BrowserAnimationsModule in the core module may lead to dysfunctional behavior

Attempting a second filter of the table using the dropdown results in no data being returned

Unexpected behavior with onKeyPress in React-Native Windows resulting in missing key press events

Angular function for downloading table cells

Adding SVG to Component

What is the reason for injecting a service into 2 modules following the Singleton Pattern?

Create a POST request following a GET request and handle it in Angular 2

Expanding worldwide in TypeScript

Store a new JSON item in the localStorage

Tips for implementing an automatic refresh functionality in Angular

Struggling to Decode Octet-stream Data in Angular 6 HttpClient: Encountering Parsing Failure with Error Prompt: "Failed to parse HTTP response for..."

I am facing an issue with my useFetch hook causing excessive re-renders

Issues encountered while developing a ReactJS application using TypeScript

Exploring the power of Prosemirror with NextJS through Tiptap v2

Exploring Angular2: Incorporating External Plugins with AngularCLI (webpack)

Exploring Typescript for Efficient Data Fetching

Using Typescript to incorporate Next.js on Firebase Functions