Exploring the <> syntax in Angular2 with Typescript

Question

Exploring the <> syntax in Angular2 with Typescript

I am brand new to Angular2 and struggling to grasp the < > syntax :

For instance, in example 1 (found at https://angular.io/docs/ts/latest/guide/dependency-injection.html):

let mockService = <HeroService> {getHeroes: () => expectedHeroes }

Another example can be seen in example 2 (taken from https://angular.io/docs/ts/latest/guide/template-syntax.html)

deleteRequest = new EventEmitter<Hero>();

I would greatly appreciate any assistance or direction towards a more detailed explanation.

angular typescript

Answer 1

Answer №1

<CharacterService> {getCharacters: () => expectedCharacters }

is an example of a type assertion for the CharacterService class. The object returned will adhere to the structure defined within this class.

new EventEmitter<Character>();

demonstrates how to specify the type parameter of the EventEmitter class using generics, indicating that it will handle instances of type Character. This ensures that only objects with the correct type can be passed into the emit method of the EventEmitter (refer to https://github.com/angular/angular/blob/master/modules/%40angular/facade/src/async.ts#L80).

For further information, you may refer to the following resources:

https://www.typescriptlang.org/docs/handbook/generics.html

Answer 2

<CharacterService> {getCharacters: () => expectedCharacters }

is an example of a type assertion for the CharacterService class. The object returned will adhere to the structure defined within this class.

new EventEmitter<Character>();

demonstrates how to specify the type parameter of the EventEmitter class using generics, indicating that it will handle instances of type Character. This ensures that only objects with the correct type can be passed into the emit method of the EventEmitter (refer to https://github.com/angular/angular/blob/master/modules/%40angular/facade/src/async.ts#L80).

For further information, you may refer to the following resources:

https://www.typescriptlang.org/docs/handbook/generics.html

Answer 3

Answer №2

These are known as "type assertions" and can be found in the TypeScript manual.

Just a quick tip, it's preferable not to refer to them as "casts". Instead, you are essentially communicating to the compiler that a value should be treated as a specific type. The compiler will throw errors if you try to assign a type that is incompatible. Put simply, the asserted type needs to be more specific. Also consider using the alternative syntax as Type after the value for better readability and to avoid conflicts with React.

Answer 4

These are known as "type assertions" and can be found in the TypeScript manual.

Just a quick tip, it's preferable not to refer to them as "casts". Instead, you are essentially communicating to the compiler that a value should be treated as a specific type. The compiler will throw errors if you try to assign a type that is incompatible. Put simply, the asserted type needs to be more specific. Also consider using the alternative syntax as Type after the value for better readability and to avoid conflicts with React.

Exploring the <> syntax in Angular2 with Typescript

Answer №1

Answer №2

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