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

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