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Question

What is the proper way to map enum in typescript?

For instance I am playing around with an online typescript code editor and this works fine:

class Message
{
    name: string;
    min: number;
    max: number;
    messageType: MessageType;
}

enum MessageType
{
    none,
    email,
    sms

}

var jsonObj = {
    "name": "some name",
    "min": 0,
    "max": 10,
    "messageType": MessageType.email

}

var messageInstance: Message = <Message>jsonObj;

console.log(messageInstance);

However, in my IDE MessageType.email shows an error of "value expected" if I use it in a json file.

If I try:

"messageType": "MessageType.email"

In the online code editor then that generates an error.

I am just getting started and can't find any clear instructions on how this should be done.

edit:

I just realised enums are number based so "messageType": 2 or whatever corresponding number would be the correct way to go.

Is there any way to make the enum readable in the json file (ie something like MessageType.email as a value) as when viewed alone the json file doesn't have the enum definitions so might be confusing so I'd rather do it that way if possible..

Answer 1

For TypeScript 2.4+:

You can use string enums instead of a numeric enum:

enum MessageType
{
    none = "none",
    email = "email",
    sms = "sms"
}

For older versions of TypeScript:

You can convert an enum value to a string using the enum 's indexer:

const messageTypeAsString = MessageType[MessageType.email];

Going the other way works too:

const messageType: MessageType = MessageType[messageTypeAsString];

As far as I know there is no way to automate this conversion when serializing/deserializing JSON.

The other option is to skip enum entirely and use static string s instead:

class MessageType {
    static readonly none = 'none';
    static readonly email = 'email';
    static readonly sms = 'sms';
}
type MessageTypeValue = 'none' | 'email' | 'sms'; 

const messageType: MessageTypeValue = MessageType.none;