Typescript enum, interface and mapping

Question

In TypeScript, in an array or similar data structure, how can I map a string to an id, while ensuring that only a certain range of ids is allowed?

Here is what I want to do. This works fine. However, I am wondering if there is a more concise way of achieving this?

enum ETypeId {
    alpha  = "a",
    beta   = "b",
    gamma  = "g"
}

interface IType {
    id:     ETypeId,
    title:  string,
}

myTypes: IType[] = [
    { id: ETypeId.alpha, title: "Alpha" },
    { id: ETypeId.beta,  title: "Beta"  },
    { id: ETypeId.gamma, title: "Gamma" }
];

As is, I have to do the following to get from the id to the title:

function getTypeForTypeId( typeId: ETypeId ): IType {
    return myTypes.find( type => type.id == typeId );
}

Can I use a different data structure that makes some of the above code more concise, or is this already as good as it gets?

Explanation:

"a" is what gets stored in my database
ETypeId.alpha is how I access it in my code
"Alpha" is what gets displayed to the user.

mykhailo.romaniuk · Accepted Answer · 2018-04-27 20:06:45Z

14

Agree with Sergi Dote Teixidor's answer that Map is the best option for such problem. However, based on the described problem, I think that it could be simplified to Map<ETypeId, string>:

enum ETypeId {
    alpha  = "a",
    beta   = "b"
}

const types: Map<ETypeId, string> = new Map( [
   [ ETypeId.alpha, "Alpha" ],
   [ ETypeId.beta, "Beta" ],
]);

Just in case you want to initialize your structure once and make TypeScript protect you from changing values inside your map:

enum ETypeId {
    alpha  = "a",
    beta   = "b"
}

interface ReadonlyMap<TKey, TValue> {
    get(key: TKey):TValue;
}

const types: ReadonlyMap<ETypeId, string> = new Map( [
   [ ETypeId.alpha, "Alpha" ],
   [ ETypeId.beta, "Beta" ],
]);

// Static analyzer error if you try to change the value:
types.set(ETypeId.alpha, "NewValue");

answered Apr 27, 2018 at 20:06

mykhailo.romaniuk

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Sergi Dote Teixidor · Accepted Answer · 2018-04-27 19:31:06Z

11

you can use a map:

you can retrieve directly any element
you can loop all elements if you want

example:

enum ETypeId {
    alpha  = "a",
    beta   = "b",
    gamma  = "g"
}

interface IType {
    id:     ETypeId,
    title:  string,
}

const myMap: Map<string, IType> = new Map( [
   [ ETypeId.alpha,  { id: ETypeId.alpha, title: "Alpha" } ],
   [ ETypeId.beta,  { id: ETypeId.beta,  title: "Beta"  } ],
   [ ETypeId.gamma, { id: ETypeId.gamma, title: "Gamma" } ]
]);

console.log(myMap.get(ETypeId.alpha)) // -> {id: "a", title: "Alpha"}

answered Apr 27, 2018 at 19:31

Sergi Dote Teixidor

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