What is the significance of using private or public in Angular's dependency injection mechanism?

Question

What is the significance of using private or public in Angular's dependency injection mechanism?

It has come to my attention that an angular class fails to recognize an injected service unless it is explicitly defined with scope.

The following code does not function as expected:

constructor(router: Router) {}

However, this code works correctly:

constructor(private router: Router) {}

I am curious as to why this discrepancy exists. I had assumed that without explicit scope definition, properties default to public, similar to class properties. However, it appears this is not the case in this scenario.

angular typescript dependency-injection scope angular-services

Answer 1

Answer №1

When you declare something in your constructor, it is treated as a parameter. It's a feature of TypeScript that allows you to assign an accessor to it. For example:

constructor(private router: Router) {}

This is equivalent to the following ES6 code:

constructor(router) {
  this.router = router;
}

However, if you specify dependency injection like this:

constructor(router: Router) {
  // router is only accessible within this scope
}

The difference is that the value is only accessible inside the constructor, not within the class instance. This is because it is defined within the constructor's {} scope. On the other hand, a class field declared in the class' {} scope is accessible throughout the entire class.

Answer 2

When you declare something in your constructor, it is treated as a parameter. It's a feature of TypeScript that allows you to assign an accessor to it. For example:

constructor(private router: Router) {}

This is equivalent to the following ES6 code:

constructor(router) {
  this.router = router;
}

However, if you specify dependency injection like this:

constructor(router: Router) {
  // router is only accessible within this scope
}

The difference is that the value is only accessible inside the constructor, not within the class instance. This is because it is defined within the constructor's {} scope. On the other hand, a class field declared in the class' {} scope is accessible throughout the entire class.

Answer 3

Answer №2

In the realm of programming, there are two types of parameters - the first simply acts as a variable, while the second not only acts as a parameter but also initializes and assigns a private field within the code. For example, using public router: Router would be a parameter that both declares and sets a public field. Dependency injection (DI) operates on the assumption that the instance will preserve the injected object throughout its lifespan.

Answer 4

In the realm of programming, there are two types of parameters - the first simply acts as a variable, while the second not only acts as a parameter but also initializes and assigns a private field within the code. For example, using public router: Router would be a parameter that both declares and sets a public field. Dependency injection (DI) operates on the assumption that the instance will preserve the injected object throughout its lifespan.

Answer 5

Answer №3

Utilizing a private variable within the constructor parameter in Angular is not only a widely accepted practice that encourages encapsulation, but also takes advantage of TypeScript's automatic property initialization and fits seamlessly with Angular's dependency injection system. This approach plays a significant role in creating a more organized and sustainable codebase.

Answer 6

Utilizing a private variable within the constructor parameter in Angular is not only a widely accepted practice that encourages encapsulation, but also takes advantage of TypeScript's automatic property initialization and fits seamlessly with Angular's dependency injection system. This approach plays a significant role in creating a more organized and sustainable codebase.

What is the significance of using private or public in Angular's dependency injection mechanism?

Answer №1

Answer №2

Answer №3

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