Cast int to enum strings in Typescript

Question

I get from a RESTful Service the following data:

[
  {
    "id": 42,
    "type": 0,
    "name": "Piety was here",
    "description": "Bacon is tasty, tofu not, ain't nobody like me, cause i'm hot...",
  }...

And I'm mapping with this class:

export enum Type {
  Info,
  Warning,
  Error,
  Fatal,
}


export class Message{
  public id: number;
  public type: Type:
  public name: string;
  public description: string;
}

But when I access 'type' in Angular2 I get only a int value. But I'd like to get a string value.

e.g:

'message.type=0'
{{message.type}} => should be Info
'message.type=1'
{{message.type}} => should be Warning

Solution 1

Enums in TypeScript are numbers at runtime, so message.type will be 0, 1, 2 or 3.

To get the string value, you need to pass that number into the enum as an index:

Type[0] // "Info"

So, in your example, you'll need to do this:

Type[message.type] // "Info" when message.type is 0

Docs

Solution 2

Enums in TypeScript are objects at runtime that have properties that go from int -> string and from string -> int for all possible values.

To access the string value you will need to call:

Type[0] // "Info"

Make sure that you are passing the correct type into the property accessor though because chained calls can result in the following:

Type[Type.Info] // "Info"
Type[Type[Type.Info]] // 0
Type["Info"] // 0
Type[0] // "Info"

Solution 3

I think with

{{message.type}}

you just get the mapped value and not the enum. Please try following code.

{{TYPE[message.type]}}

Comments

[Franz Peter Tebartz van Elst]

How can I do that? I'm mapping like this right now: (response => response.json() as Message[]

[James Monger]

Import Type into your file, and rather than doing message.type to get the value, do Type[message.type]. You do this where you want the string value

[Admin]

Unfortunately, Type will not be available inside a template, unless you add it as a property to the component class as public Type = Type;.

[Vodenjak]

Can anyone tell me why if i do Type[message.type] in my case, in debugger I see an error because Type is undefined (it's imported properly to this .ts file)?

[gajo357]

How to check if a number is part of the enum, f.x. check for number 3000 before returning Type[3000]?

[Teddy Sterne]

@gajo357 You can use the in operator to test if 3000, or any value/key exists in the enum. Example const has3000 = 3000 in Type