Generate TypeScript types from JSON Schema with json-schema-to-typescript: working versions (tested 2026-10-15)

{
  "name": "json-schema-to-typescript-codegen",
  "private": true,
  "type": "module",
  "scripts": {
    "test": "node --import tsx --test test/*.test.ts"
  },
  "dependencies": {
    "json-schema-to-typescript": "16.0.0"
  },
  "devDependencies": {
    "@types/node": "26.6.5",
    "tsx": "4.23.15"
  }
}

import { compile, type JSONSchema } from "json-schema-to-typescript";

export const orderSchema: JSONSchema = {
  title: "Order",
  type: "object",
  additionalProperties: false,
  required: ["id", "status", "items"],
  properties: {
    id: { type: "string", description: "Order id, e.g. ord_123" },
    status: { type: "string", enum: ["pending", "paid", "shipped"] },
    note: { type: "string" },
    items: { type: "array", items: { $ref: "#/definitions/LineItem" }, minItems: 1 },
  },
  definitions: {
    LineItem: {
      type: "object",
      additionalProperties: false,
      required: ["sku", "qty"],
      properties: { sku: { type: "string" }, qty: { type: "integer", minimum: 1 } },
    },
  },
};

export async function generateTypes(schema: JSONSchema, name: string): Promise<string> {
  return compile(schema, name, {
    bannerComment: "/* Generated from JSON Schema. Do not edit. */",
    additionalProperties: false,
    strictIndexSignatures: true,
    style: { singleQuote: false, semi: true },
  });
}

import { test } from "node:test";
import assert from "node:assert/strict";
import { generateTypes, orderSchema } from "../src/codegen.ts";

test("generates interfaces with required, optional and enum fields", async () => {
  const ts = await generateTypes(orderSchema, "Order");
  assert.match(ts, /^\/\* Generated from JSON Schema\. Do not edit\. \*\//);
  assert.match(ts, /export interface Order \{/);
  assert.match(ts, /\n\s+id: string;/);
  assert.match(ts, /status: "pending" \| "paid" \| "shipped";/);
  assert.match(ts, /note\?: string;/);
  assert.match(ts, /items: \[LineItem, \.\.\.LineItem\[\]\];/);
});

test("$ref definitions become their own interfaces", async () => {
  const ts = await generateTypes(orderSchema, "Order");
  assert.match(ts, /export interface LineItem \{/);
  assert.match(ts, /sku: string;/);
  assert.match(ts, /qty: number;/);
  assert.doesNotMatch(ts, /\[k: string\]: unknown/);
});

test("descriptions become JSDoc comments", async () => {
  const ts = await generateTypes(orderSchema, "Order");
  assert.match(ts, /\/\*\*\n\s+\* Order id, e\.g\. ord_123\n\s+\*\/\n\s+id: string;/);
});

test("open objects keep an index signature when allowed", async () => {
  const ts = await generateTypes({ title: "Meta", type: "object", additionalProperties: true, properties: { a: { type: "number" } } }, "Meta");
  // strictIndexSignatures adds "| undefined" so lookups by unknown keys stay honest.
  assert.match(ts, /\[k: string\]: unknown \| undefined;/);
});