typescript type object with string keys and content defined by interface

Question

my data has this structure:

groups = {
    someGroupName: {
        total: 30,
        count: 3,
        average: 10
    },
    someOtherGroupName: {
        total: 60,
        count: 3,
        average: 20
    }
}

I can write an interface for the nested part:

interface Stats {
    total: number,
    count: number,
    average: number
}

but how can I set a type for groups as a whole? I do not know what groups are coming in. I just know that it will be a groupname as the key and the stats object as the value.

Titian Cernicova-Dragomir · Accepted Answer · 2018-06-21 16:18:23Z

29

You can use an index signature to tell typescript that the object is indexable by any string but all values in the object are of a certain type:

interface Stats {
    total: number,
    count: number,
    average: number
}

interface Groups {
    [name: string] : Stats
}

let groups: Groups = {
    someGroupName: {
        total: 30,
        count: 3,
        average: 10
    },
    someOtherGroupName: {
        total: 60,
        count: 3,
        average: 20
    }
}

let someGroupName = groups['someGroupName'] //someGroup is Stats
groups['someGroupName'] = 0 // invalid 0 is not of type Stats

answered Jun 21, 2018 at 16:18

Titian Cernicova-Dragomir

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1 Comment

Clark Over a year ago

Could you use a Record<string, Stats> as opposed to the Groups Interface?

Abraham · Accepted Answer · 2022-12-19 15:39:28Z

21

Simpler way

You can use {[key:string]:string} as a type for any object with string values and string keys.

type strObj = {[key:string]:string}

const sample:strObj = {
    one:"text1",
    two:"text2"
}

For nested Object

And if it is a nested object, you can nest the type in place of the second string at the end.

{[key:string]: string} ==> {[key:string]: {[key:string]:string}}

Hence,

type strObj = {[key:string]:{[key:string]:string}}
const sample:strObj = {
    one:{
        sub:"text1"
    },
    two:{
        sub:"text2"
    }
}

edited Dec 19, 2022 at 15:39

answered Nov 5, 2021 at 0:08

Abraham

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