Can an Angular 2 module export an interface?

Question

Can an Angular 2 module export an interface?

While attempting to export an interface in a NgModule-declaration, I encountered an error message in my editor (Visual Studio Code) stating:

[ts] 'MyInterface' only refers to a type, but is being used as a value here.

Below is the code snippet containing the issue labeled as Edit-1:

import { NgModule }           from '@angular/core';
import { CommonModule }       from '@angular/common';
import { FormsModule }        from '@angular/forms';
import { MaterialModule }     from '@angular/material';
import { MyInterface }        from './my.interface';
import { MyService }          from './my.service';

@NgModule({
  imports:      [ CommonModule, FormsModule,  MaterialModule.forRoot()  ],
  declarations: [ MyInterface],//<- this is causing the message
  exports:      [ MyInterface],
  providers:    [ MyService ]
})
export class MyModule { }

One possible explanation I came across in a Stack Overflow post was that "interfaces are erased at runtime in TypeScript." As I am currently in the process of refactoring my app to utilize feature modules, I am unable to test this assumption at present: Can interfaces only be used by importing them from './mypathto/my.interface'?

angular typescript

Answer 1

Answer №1

Interfaces cannot be exported directly. The only items that can be exported are:

Other modules
Components
Directives
Pipes

In Angular, the concept of NgModule should not be confused with a typescript module. To allow third parties to use your interface in their modules, you need to create a .d.ts definition file along with your module.

If you need to use an interface from another NgModule within your project, simply import it using:

import {InterfaceName} from 'path/to/ngmodule/to/interface';

Remember not to include interfaces in the declarations array, as this is reserved for pipes, components, and directives.

To make your interface accessible outside of a library, add it to the export list in your index.ts:

export {InterfaceName} from 'path/to/ngmodule/to/interface';

Answer 2

Interfaces cannot be exported directly. The only items that can be exported are:

Other modules
Components
Directives
Pipes

In Angular, the concept of NgModule should not be confused with a typescript module. To allow third parties to use your interface in their modules, you need to create a .d.ts definition file along with your module.

If you need to use an interface from another NgModule within your project, simply import it using:

import {InterfaceName} from 'path/to/ngmodule/to/interface';

Remember not to include interfaces in the declarations array, as this is reserved for pipes, components, and directives.

To make your interface accessible outside of a library, add it to the export list in your index.ts:

export {InterfaceName} from 'path/to/ngmodule/to/interface';

Answer 3

Answer №2

Actually, exporting an interface is possible, but not in the way you are attempting.

To create an interfaces.ts file, use the command:

ng g interface <interface_name>

Here's an example of what an interface file might look like:

export interface Product { id?: string; name: string; price: number; ... }
export interface Order { orderId?: string; products: Product[]; total: number; ...}

Once you've customized the file to your specifications, you can import individual or multiple interfaces like this:

import { Product } from './interfaces';

or

import * as interfaces from './interfaces'; 
// then you would access interfaces.Product

If you happen to know how to globally share interfaces, please share your knowledge here: How to share interfaces across multiple Angular components

Answer 4

Actually, exporting an interface is possible, but not in the way you are attempting.

To create an interfaces.ts file, use the command:

ng g interface <interface_name>

Here's an example of what an interface file might look like:

export interface Product { id?: string; name: string; price: number; ... }
export interface Order { orderId?: string; products: Product[]; total: number; ...}

Once you've customized the file to your specifications, you can import individual or multiple interfaces like this:

import { Product } from './interfaces';

or

import * as interfaces from './interfaces'; 
// then you would access interfaces.Product

If you happen to know how to globally share interfaces, please share your knowledge here: How to share interfaces across multiple Angular components

Can an Angular 2 module export an interface?

Answer №1

Answer №2

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