Importing JSON files as const?

[Mqxx]

Is it possible to import JSON files, so that I don't loose the literal information?

What I want to archive

If I have this TS array in a file:

my_array.ts

export default [
  "foo",
  "bar",
  "baz"
] as const; // <-- This is the important part

And then:

index.ts

import myArray from 'my_array.ts'

type MyArrayUnion = typeof myArray[number] // <-- this type is ('foo' | 'bar' | 'baz') like I want

How the JSON import works

If I have this JSON array in a file:

my_array.json

[
  "foo",
  "bar",
  "baz"
]

And I want to import it like this:

index.ts

import myArray from 'my_array.json' with {type: 'json'}

type MyArrayUnion = typeof myArray[number] // <-- this type is just "string"

The behavior of the JSON import works correctly as expected, but I want to know if, is it possible to archive the same as with the TS array and as const statement, but for the JSON import? Sadly it is not possible to cast the import using as const, as it results in the error:

A 'const' assertions can only be applied to references to enum members,
or string, number, boolean, array, or object literals.

Why I want to do this in the first place?

I want to create a function that takes the JSON file as argument and based on that argument, suggests IntelliSense for the return function. Something like this:

my_methods.json

[
  "foo",
  "bar",
  "baz"
]

index.ts

import schema from './example.json' with { type: "json" }


export function client<Schema extends string[]>(schema : Schema) {
  return {
    call: (method : Schema[number]) => {
      // do something with "method"
    }
  }
}

client(schema).call('') // <-- IntelliSense/Autocompletion for the JSON array

The actual JSON file is way more complex in structure and gets generated by an other program.

[bartlomieju]

No, it's not possible, it would have to be supported in TypeScript compiler first. I suggest to open a feature request at https://github.com/microsoft/TypeScript

[Mqxx]

Thanks for the quick answer 😊

No, it's not possible, it would have to be supported in TypeScript compiler first.

Unfortunately, I already suspected that.