Setting: Angular 5+
Source: https://angular.io/tutorial
Within the heroes.component.ts class, we see an assignment using a colon:
export class HeroesComponent implements OnInit {
heroes: Hero[];
However, in the app.component.ts class, a different assignment method is used with the equal sign:
export class AppComponent {
title = 'app';
}
What is the reason behind this difference?
Within the code snippet heroes: Hero[];, the variable heroes is declared as an array of type Hero without any initial assignment. As a result, at this point, it remains undefined.
Conversely, in the code title = 'app';, the string 'app' is explicitly assigned to the variable title. Because TypeScript can recognize 'app' as a string, there is no necessity to specify the type as title: string = 'app';. This differs from the situation with heroes, where the compiler needs more information to determine what will be assigned to the variable. In this case, you must provide guidance by specifying : Hero[] (indicating that it is an array of type Hero).
In the initial example, it is noted that the variable heroes represents an array containing objects of the type Hero; however, no specific value is assigned to this property.
On the other hand, the second example defines the title property as the string app, but neglects to specify its data type. By assigning a string value, the property is automatically typed as a string.
It is crucial to explicitly declare the type of any variable to avoid ending up with generic any variables. Furthermore, it is recommended to initialize variables to ensure clarity; otherwise, be aware that they will default to undefined until assigned a value.
In the feedback provided by @Richards, it was noted that:
During your development process with Typescript, additional types are incorporated above JavaScript to enhance your coding and debugging experience.
When you see heroes: Hero[];, it indicates that heroes is an array belonging to the type Hero. No value is currently assigned, and heroes remains undefined
On the other hand, title = 'app'; signifies that title is a variable containing the value 'app', categorized as a string
Remember, the = operator is solely used for value assignment.
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