CODEWITHSUNDEEP
typescripttypes
Algorithmic Canary
Algorithmic Canary

Reputation: 740

constrain type of values of an object in Typescript

In typescript, how to I write the type signature for plain old javascript object that can have any key, but the values are always strings. For example, {a:"foo"}, {b:"bar"} are both valid values but {a:[1,2,3]} and {b:3} are not.

I want to be able to write something like

let foo : {*: string} = {a: "foo"}

Currently, I am using any to achieve this, but that isn't as precise as I would like.

Upvotes: 1

Views: 1354

Answers (2)

Icepickle
Icepickle

Reputation: 12806

I am guessing you are looking at a enum definition for the values of your properties.

I think you can declare it something like:

let foo: { [k: string]: 'foo' | 'bar' | 'type'};

foo.a = 'bar';
foo.d = 'type';
foo.q = 'bar';
foo.c = 'let'; // shows as not assignable

You can see it in this typescript fiddle

Upvotes: 0

Fenton
Fenton

Reputation: 251262

You can use an index signature to state that all values will be a string...

type Example = { [key: string]: string };

Example:

type Example = { [key: string]: string };

const a: Example = {
    "anything": "any string", // ok
    anotherkey: "a string", // ok
    thirdKey: 1 // Error
};

Upvotes: 1

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