Validate JSON against TypeScript

Question

We use JSON files to configure some of our web applications and obviously mistakes are being made in field names etc.

Is it possible to validate the JSON file using a TypeScript definitions? Or should we migrate our configuration to other format?

We use both Intellij and VSCode for development.

Example definition:

interface AppConfig {
  field1: number;
  field2?: string;
  field3: number[];
}

Example configuration:

{
  "field": 1,
  "field3": 2
}

Example validation result:

TS2322: Type '{ field: number; field3: number[]; }' is not assignable to type 'AppConfig'.
TS2322: Type 'number' is not assignable to type 'number[]'.

When do you want to perform the check? At compile time? Where do you use the json? Do you load it over http or do you import it in a javascript file? — MaartenDev
– MaartenDev, Commented Apr 25, 2022 at 8:30
Do you have code examples of what one JSON file might look like? Are there fields that must be included vs fields that are optional? — Sebastian Salletmayer
– Sebastian Salletmayer, Commented Apr 25, 2022 at 8:41
@MaartenDev Preferably automatically on each edit (similarly as lint checks) or on demand. But I wanted to know the possibilities so I did not want to restrict it in the beginning. — Jan Málek
– Jan Málek, Commented Apr 25, 2022 at 11:41
@SebastianSalletmayer I edited my question, hopefully that answers your question — Jan Málek
– Jan Málek, Commented Apr 25, 2022 at 11:55

fknx · Accepted Answer · 2022-04-25 12:11:48Z

1

A solution could be to create JSON Schema files according to your TypeScript interfaces and then let the IDE perform the validation of the JSON files according to the schemata. IntelliJ offers such a validation (including auto-complete) with their JSON support.

If you don't want to create the schemata yourself, you can generate them from your TypeScript interfaces using the typescript-json-schema NPM package.

answered Apr 25, 2022 at 12:11

fknx

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2 Comments

Jan Málek Over a year ago

I have been playing with this for about 3 hours now and it almost clicks, but not quite: When I run it using typescript-json-schema appconfig.ts * -o appconfig.schema.json --required --noExtraProps The result with my ts contains unnecessary nested "definitions": { "AppConfig": { which makes it unusable. Do you have any idea of how to either get rid of it? Without this nesting everything about it works just perfectly.

fknx Over a year ago

@JanMálek This is caused by the * in your command. If you specify the type explicitly it should yield the desired result: typescript-json-schema appconfig.ts AppConfig -o appconfig.schema.json --required --noExtraProps

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