Deciphering the Sequence of Definitions in TypeScript and Angular JS

As a newcomer to Angular JS and TypeScript, I have encountered an issue while going through the hero tutorial. The problem arises when defining the Hero class between @Component and AppComponent instead of at the beginning or end of the file. This causes a runtime exception with the message "No Directive annotation found on AppComponent". I lack the necessary understanding of TypeScript and Angular JS to comprehend why this sequence is crucial. Is there a special syntax required when placing the Hero definition in the middle? Your guidance would be greatly appreciated. You can find the Plunker for the tutorial here. Thank you!

Answer №1

@Directive or any other similar construct that begins with an @ symbol serves as an annotation in programming languages. These annotations are linked to the code element (such as a class or variable) immediately after them, and provide metadata about that particular piece of code. In this scenario, @Directive indicates that the attached class is an Angular directive.

If you place the User class between @Directive and ContactComponent, it signifies that User, not ContactComponent, is recognized as an Angular directive since User directly follows @Directive.

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