How to access a dynamic key in Typescript

Question

I have the following code:

type StringMapType<K extends string[]> = Record<K[number], string>

const en = {
  'general': {
    'hi': {
      string: 'Aenean ullamcorper neque id elementum commodo. {{firstName}}',
      params: ['firstName']
    },
     'bye': {
      string: 'Aenean ullamcorper neque id elementum commodo.',
      params: null
    }
  },
} as const


const getLocalizedString = <ContextType extends keyof typeof en, KeyType extends keyof typeof en[ContextType], ParamsType extends typeof en[ContextType][KeyType]['params']>(context: ContextType, key: KeyType, ...params: typeof en[ContextType][KeyType]['params'] extends null ? [undefined?] : [StringMapType<ParamsType>]) => {
  // Code that would return the correct value
}


getLocalizedString('general', 'hi', {
  firstName: 'John'
})

For some reason, I'm getting an error on the ParamsType saying that Type '"params"' cannot be used to index type. The code itself works and does what I want, just wondering if there is any way how to get around this error.

Demo

Thanks in advance

Solution

Based on @seti's answer

const en = {
  general: {
    hi: {
      string: 'hi, {{firstName}}',
      params: ['firstName'] as const,
    },
    bye: {
      string: 'bye',
      params: [] as const,
    }
  },
} as const

const translations = {
  en,
} as const

const language = 'en'

type CT = keyof typeof en
type KT = keyof typeof en[CT]
type ParamsType<KeyType extends KT> = typeof en[CT][KeyType]['params'][number]
type StringType<KeyType extends KT> = typeof en[CT][KeyType]['string']

const getLocalizedString = <ContextType extends CT = CT, KeyType extends KT = KT>(
  context: ContextType,
  key: KeyType,
  ...params: ParamsType<KeyType> extends undefined ? [undefined?] : [{ [key in ParamsType<KeyType>]: string }]
): StringType<KeyType> => {

  return translations[language][context][key].string
}

getLocalizedString('general', 'hi', {firstName: 'John'})

getLocalizedString('general', 'bye')

Why do you need to capture the valid keys at the type level? — decorator-factory
– decorator-factory, Commented May 19, 2022 at 11:50

Seti · Accepted Answer · 2022-05-19 23:32:11Z

1

I have wrote Example Solution for you, and have split the declarations into several parts

So this monstrocity:

type StringMapType<K extends string[]> = Record<keyof K[number] & string, string>

const en = {
  'general': {
    'hi': {
      string: 'Aenean ullamcorper neque id elementum commodo. {{firstName}}',
      params: ['firstName', 'test'] as const
    },
     'bye': {
      string: 'Aenean ullamcorper neque id elementum commodo.',
      params: ['x'] as const
    }
  },
} as const;


type X = keyof typeof en;
type Y = keyof typeof en[X];
type W = typeof en[X][Y]['string'];
type F<YY extends Y> = typeof en[X][YY]['params'][number];
type G<YY extends K<Y>> = {[key in F<YY>]: string};
type K<YY extends Y> = YY;


const getLocalizedString = <KK extends Y = Y, GG = Required<{[key in F<KK>]: string}>, XX extends X = X>(context: XX, key: KK, ...params: GG[]) => {

}



getLocalizedString('general', 'hi', {
  firstName: 'John',
  aaa: 'a',
});

getLocalizedString('general', 'bye', {
 'y': '',
});

From that you can experiment more. Only one issue with this - it do not check against wrong, but you have some starting point now

answered May 19, 2022 at 23:32

Seti

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3 Comments

Kristjan Vool Over a year ago

Thanks a ton! This was pretty much all I needed, did a couple of modifications to check for errors and got it working great!

Seti Over a year ago

Can you share yours code so we all could see it in the end?^^

Kristjan Vool Over a year ago

edited the question with a solution :)

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