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Creating a type which defines keys of an object containing a specific nested property

TypeScript: Creating an empty typed container arrayDefine objects to only contain elements of specific typeAngular2 object property typed as “number” changes to stringType for extracting nested object keysTypeScript type with properties of an object containing a specific typeHow to describe type that ensures specific property on nested objectsDefine in typescript object type to contain a specific property keyDefine a type for all possible object property typesTypescript error, how to correct this: Element implicitly has an 'any' type because typeTyping a record of a known type

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1

I have an interesting case where it would be very useful to dynamically define types from a central JSON data store. Let me explain.

I have a json file that contains a list of brands

// brands.json

 "Airbus": 
 "keywords": ["A320", "A380"],
 "type": ["planes"]
 ,
 "Jaguar": 
 "keywords": ["fiesta"],
 "origin": "UK",
 "type": ["cars", "glasses"]
 ,
 "Nissan": 
 "keywords": ["qashqai"],
 "type": ["cars"]
 

Then I have my type definitions:

import brands from "./brands.json

type BrandNames= keyof typeof brands ;

type Brands = 
 [P in BrandNames]: 
 keywords: string[];
 origin?: string;
 type: string[];
 
;

I have created a type CompanieNames which is automatically generated and is equal to "Airbus" | "Jaguar" | "Nissan".

So far so good...

Now, I want to create a type CarBrands, which will be equal to "Jaguar" | "Nissan".

Doing type CarBrands = Exclude<CompanieNames, "Airbus">; would work, but this is not dynamic.

So instead, I need to filter out all keys from Brands which have a nested type property that doesn't contain the string "cars".

Is it possible to do that?

typescript

share|improve this question

edited Mar 24 at 10:55

h-Reser

asked Mar 24 at 10:02

h-Reserh-Reser

377

add a comment | 

1

I have an interesting case where it would be very useful to dynamically define types from a central JSON data store. Let me explain.

I have a json file that contains a list of brands

// brands.json

 "Airbus": 
 "keywords": ["A320", "A380"],
 "type": ["planes"]
 ,
 "Jaguar": 
 "keywords": ["fiesta"],
 "origin": "UK",
 "type": ["cars", "glasses"]
 ,
 "Nissan": 
 "keywords": ["qashqai"],
 "type": ["cars"]
 

Then I have my type definitions:

import brands from "./brands.json

type BrandNames= keyof typeof brands ;

type Brands = 
 [P in BrandNames]: 
 keywords: string[];
 origin?: string;
 type: string[];
 
;

I have created a type CompanieNames which is automatically generated and is equal to "Airbus" | "Jaguar" | "Nissan".

So far so good...

Now, I want to create a type CarBrands, which will be equal to "Jaguar" | "Nissan".

Doing type CarBrands = Exclude<CompanieNames, "Airbus">; would work, but this is not dynamic.

So instead, I need to filter out all keys from Brands which have a nested type property that doesn't contain the string "cars".

Is it possible to do that?

typescript

share|improve this question

edited Mar 24 at 10:55

h-Reser

asked Mar 24 at 10:02

h-Reserh-Reser

377

add a comment | 

I have an interesting case where it would be very useful to dynamically define types from a central JSON data store. Let me explain.

I have a json file that contains a list of brands

// brands.json

 "Airbus": 
 "keywords": ["A320", "A380"],
 "type": ["planes"]
 ,
 "Jaguar": 
 "keywords": ["fiesta"],
 "origin": "UK",
 "type": ["cars", "glasses"]
 ,
 "Nissan": 
 "keywords": ["qashqai"],
 "type": ["cars"]
 

Then I have my type definitions:

import brands from "./brands.json

type BrandNames= keyof typeof brands ;

type Brands = 
 [P in BrandNames]: 
 keywords: string[];
 origin?: string;
 type: string[];
 
;

I have created a type CompanieNames which is automatically generated and is equal to "Airbus" | "Jaguar" | "Nissan".

So far so good...

Now, I want to create a type CarBrands, which will be equal to "Jaguar" | "Nissan".

Doing type CarBrands = Exclude<CompanieNames, "Airbus">; would work, but this is not dynamic.

So instead, I need to filter out all keys from Brands which have a nested type property that doesn't contain the string "cars".

Is it possible to do that?

typescript

share|improve this question

edited Mar 24 at 10:55

h-Reser

asked Mar 24 at 10:02

h-Reserh-Reser

377

// brands.json

 "Airbus": 
 "keywords": ["A320", "A380"],
 "type": ["planes"]
 ,
 "Jaguar": 
 "keywords": ["fiesta"],
 "origin": "UK",
 "type": ["cars", "glasses"]
 ,
 "Nissan": 
 "keywords": ["qashqai"],
 "type": ["cars"]
 

import brands from "./brands.json

type BrandNames= keyof typeof brands ;

type Brands = 
 [P in BrandNames]: 
 keywords: string[];
 origin?: string;
 type: string[];
 
;

share|improve this question

edited Mar 24 at 10:55

h-Reser

asked Mar 24 at 10:02

h-Reserh-Reser

377

share|improve this question

edited Mar 24 at 10:55

h-Reser

asked Mar 24 at 10:02

h-Reserh-Reser

377

asked Mar 24 at 10:02

h-Reserh-Reser

377

asked Mar 24 at 10:02

h-Reserh-Reser

377

1 Answer
1

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oldest

votes

2

If the types of the string literal types were preserved, we could do what you want (ie extract only the brands that have car in the types field). Typescript will however widen the types of the values in the types array to string so this information is lost to us when we actually look at the type of the json object.

Just for fun, using the as const in 3.4 (unreleased yet) to preserve all string literal types, this is what the solution would look like:

let data = 
 "Airbus": 
 "keywords": ["A320", "A380"],
 "type": ["planes"]
 ,
 "Jaguar": 
 "keywords": ["fiesta"],
 "origin": "UK",
 "type": ["cars", "glasses"]
 ,
 "Nissan": 
 "keywords": ["qashqai"],
 "type": ["cars"]
 
 as const;

type Data = typeof data;
type CarBrands = 
 [P in keyof Data]: 'cars' extends Data[P]['type'][number] ? P : never
[keyof Data]

Again the above does not work for imported json modules because typescript will not preserve the literal types in the string arrays and there is no way to tell it to do so at the time of writing.

share|improve this answer

answered Mar 24 at 13:59

Titian Cernicova-DragomirTitian Cernicova-Dragomir

80.9k46177

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I have the possibility to convert my json file to a typescript file in this case. And since version 3.4 is only a couple days away, your proposition is actually very helpful! Thanks
  
  – h-Reser
  Mar 24 at 15:13
  

  
  
  
  

add a comment | 

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2

If the types of the string literal types were preserved, we could do what you want (ie extract only the brands that have car in the types field). Typescript will however widen the types of the values in the types array to string so this information is lost to us when we actually look at the type of the json object.

Just for fun, using the as const in 3.4 (unreleased yet) to preserve all string literal types, this is what the solution would look like:

let data = 
 "Airbus": 
 "keywords": ["A320", "A380"],
 "type": ["planes"]
 ,
 "Jaguar": 
 "keywords": ["fiesta"],
 "origin": "UK",
 "type": ["cars", "glasses"]
 ,
 "Nissan": 
 "keywords": ["qashqai"],
 "type": ["cars"]
 
 as const;

type Data = typeof data;
type CarBrands = 
 [P in keyof Data]: 'cars' extends Data[P]['type'][number] ? P : never
[keyof Data]

Again the above does not work for imported json modules because typescript will not preserve the literal types in the string arrays and there is no way to tell it to do so at the time of writing.

share|improve this answer

answered Mar 24 at 13:59

Titian Cernicova-DragomirTitian Cernicova-Dragomir

80.9k46177

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I have the possibility to convert my json file to a typescript file in this case. And since version 3.4 is only a couple days away, your proposition is actually very helpful! Thanks
  
  – h-Reser
  Mar 24 at 15:13
  

  
  
  
  

add a comment | 

2

If the types of the string literal types were preserved, we could do what you want (ie extract only the brands that have car in the types field). Typescript will however widen the types of the values in the types array to string so this information is lost to us when we actually look at the type of the json object.

Just for fun, using the as const in 3.4 (unreleased yet) to preserve all string literal types, this is what the solution would look like:

let data = 
 "Airbus": 
 "keywords": ["A320", "A380"],
 "type": ["planes"]
 ,
 "Jaguar": 
 "keywords": ["fiesta"],
 "origin": "UK",
 "type": ["cars", "glasses"]
 ,
 "Nissan": 
 "keywords": ["qashqai"],
 "type": ["cars"]
 
 as const;

type Data = typeof data;
type CarBrands = 
 [P in keyof Data]: 'cars' extends Data[P]['type'][number] ? P : never
[keyof Data]

Again the above does not work for imported json modules because typescript will not preserve the literal types in the string arrays and there is no way to tell it to do so at the time of writing.

share|improve this answer

answered Mar 24 at 13:59

Titian Cernicova-DragomirTitian Cernicova-Dragomir

80.9k46177

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I have the possibility to convert my json file to a typescript file in this case. And since version 3.4 is only a couple days away, your proposition is actually very helpful! Thanks
  
  – h-Reser
  Mar 24 at 15:13
  

  
  
  
  

add a comment | 

If the types of the string literal types were preserved, we could do what you want (ie extract only the brands that have car in the types field). Typescript will however widen the types of the values in the types array to string so this information is lost to us when we actually look at the type of the json object.

Just for fun, using the as const in 3.4 (unreleased yet) to preserve all string literal types, this is what the solution would look like:

let data = 
 "Airbus": 
 "keywords": ["A320", "A380"],
 "type": ["planes"]
 ,
 "Jaguar": 
 "keywords": ["fiesta"],
 "origin": "UK",
 "type": ["cars", "glasses"]
 ,
 "Nissan": 
 "keywords": ["qashqai"],
 "type": ["cars"]
 
 as const;

type Data = typeof data;
type CarBrands = 
 [P in keyof Data]: 'cars' extends Data[P]['type'][number] ? P : never
[keyof Data]

Again the above does not work for imported json modules because typescript will not preserve the literal types in the string arrays and there is no way to tell it to do so at the time of writing.

share|improve this answer

answered Mar 24 at 13:59

Titian Cernicova-DragomirTitian Cernicova-Dragomir

80.9k46177

let data = 
 "Airbus": 
 "keywords": ["A320", "A380"],
 "type": ["planes"]
 ,
 "Jaguar": 
 "keywords": ["fiesta"],
 "origin": "UK",
 "type": ["cars", "glasses"]
 ,
 "Nissan": 
 "keywords": ["qashqai"],
 "type": ["cars"]
 
 as const;

type Data = typeof data;
type CarBrands = 
 [P in keyof Data]: 'cars' extends Data[P]['type'][number] ? P : never
[keyof Data]

share|improve this answer

answered Mar 24 at 13:59

Titian Cernicova-DragomirTitian Cernicova-Dragomir

80.9k46177

answered Mar 24 at 13:59

Titian Cernicova-DragomirTitian Cernicova-Dragomir

80.9k46177

answered Mar 24 at 13:59

Titian Cernicova-DragomirTitian Cernicova-Dragomir

80.9k46177