在 Angular html 模板中访问常量枚举

Question

Assume I have a const enum:

export const enum MyConstEnum{
    Value1 = 'Value1',
    Value2 = 'Value2',
    Value3 = 'Value3'
}

Now I want to use it in my Angular template:

<span *ngIf="name === MyConstEnum.Value1">This has some value</value>

However, this is not possible, because MyConstEnum is not seen by template. So the question is how to access const enum in Angular html template?

If enum won't be const like this

export enum MyEnum{
    Value1 = 'Value1',
    Value2 = 'Value2',
    Value3 = 'Value3'
}

there is a solution to create property in templates' component

  public get MyEnumInComponent() {
    return MyEnum;
  }

and MyEnumInComponent will be accessible in HTML. However, I have const enum .

For this I cannot defined property like above. What is the solution (except changing const enum to enum )?

Answer 1

I can see on this link https://github.com/angular/angular/issues/25963 that it is known issue and it is specifically with const enum.

There is also a work arround suggested in the discussion on the url:
templateImports: [someConstant, UserStatus, isDevMode]
This would not work, but the below could:

templateImports: {someConstant, UserStatus, isDevMode}

Answer 2

It will be possible if TypeScript won't erase const enum declaration in the emitted JavaScript code.

There is dedicated compiler options preserveConstEnums for that:

tsconfig.json

{
  "compilerOptions": {
    ...
    "preserveConstEnums": true,
    ...
  },
  ...
}

Now, let's say you have

const-enum.ts

export const enum MyConstEnum {
    Value1 = 'Value1',
    Value2 = 'Value2',
    Value3 = 'Value3'
}

You can import it in component like:

import * as constEnumModule from './const-enum';

class SomeComponent {
  MyConstEnum = (constEnumModule as any).MyConstEnum;
}

It finally it should be available in your template for this component:

<span *ngIf="name === MyConstEnum.Value1">This has some value</value>

Answer 3

Assume I have a const enum:

export const enum MyConstEnum{
    Value1 = 'Value1',
    Value2 = 'Value2',
    Value3 = 'Value3'
}

Now I want to use it in my Angular template:

<span *ngIf="name === MyConstEnum.Value1">This has some value</value>

However, this is not possible, because MyConstEnum is not seen by template. So the question is how to access const enum in Angular html template?

If enum won't be const like this

export enum MyEnum{
    Value1 = 'Value1',
    Value2 = 'Value2',
    Value3 = 'Value3'
}

there is a solution to create property in templates' component

  public get MyEnumInComponent() {
    return MyEnum;
  }

and MyEnumInComponent will be accessible in HTML. However, I have const enum .

For this I cannot defined property like above. What is the solution (except changing const enum to enum )?

Answer 4

I bypassed this issue by replacing my const enum types to static properties inside classes like this:

export class MyEnum{
    static  Value1 = 'Value1',
    static  Value2 = 'Value2',
    static  Value3 = 'Value3'
}