Add exactOptionalPropertyTypes option

Author: rpnzl

README.md

@@ -139,6 +139,7 @@ See [server demo](example) and [browser demo](https://github.com/bcherny/json-sc
 | declareExternallyReferenced | boolean | `true` | Declare external schemas referenced via `$ref`? |
 | enableConstEnums | boolean | `true` | Prepend enums with [`const`](https://www.typescriptlang.org/docs/handbook/enums.html#computed-and-constant-members)? |
 | inferStringEnumKeysFromValues | boolean | `false` | Create enums from JSON enums with eponymous keys |
+| exactOptionalPropertyTypes | boolean | `false` | Append all optional property signatures with `\| undefined` so that they are strictly typed in accordance with TypeScript's [`exactOptionalPropertyTypes`](https://www.typescriptlang.org/tsconfig#exactOptionalPropertyTypes) option. |
 | format | boolean | `true` | Format code? Set this to `false` to improve performance. |
 | ignoreMinAndMaxItems | boolean | `false` | Ignore maxItems and minItems for `array` types, preventing tuples being generated. |
 | maxItems | number | `20` | Maximum number of unioned tuples to emit when representing bounded-size array types, before falling back to emitting unbounded arrays. Increase this to improve precision of emitted types, decrease it to improve performance, or set it to `-1` to ignore `maxItems`.

package-lock.json

@@ -20,6 +20,7 @@ main(
       'additionalProperties',
       'declareExternallyReferenced',
       'enableConstEnums',
+      'exactOptionalPropertyTypes',
       'format',
       'ignoreMinAndMaxItems',
       'strictIndexSignatures',

src/cli.ts

@@ -308,7 +308,8 @@ function generateInterface(ast: TInterface, options: Options): string {
           escapeKeyName(keyName) +
           (isRequired ? '' : '?') +
           ': ' +
-          type,
+          type +
+          (!isRequired && options.exactOptionalPropertyTypes ? ' | undefined' : ''),
       )
       .join('\n') +
     '\n' +

src/generator.ts

@@ -52,6 +52,12 @@ export interface Options {
    * Create enums from JSON enums with eponymous keys
    */
   inferStringEnumKeysFromValues: boolean
+  /**
+   * Append all optional property signatures with `| undefined` so that they are strictly typed in accordance with
+   * TypeScript's [`exactOptionalPropertyTypes`](https://www.typescriptlang.org/tsconfig#exactOptionalPropertyTypes)
+   * option.
+   */
+  exactOptionalPropertyTypes: boolean
   /**
    * Format code? Set this to `false` to improve performance.
    */
@@ -100,6 +106,7 @@ export const DEFAULT_OPTIONS: Options = {
   declareExternallyReferenced: true,
   enableConstEnums: true,
   inferStringEnumKeysFromValues: false,
+  exactOptionalPropertyTypes: false,
   format: true,
   ignoreMinAndMaxItems: false,
   maxItems: 20,

src/index.ts

@@ -2326,6 +2326,33 @@ Generated by [AVA](https://avajs.dev).
     }␊
     `
 
+## options.exactOptionalPropertyTypes.js
+
+> Expected output to match snapshot for e2e test: options.exactOptionalPropertyTypes.js
+
+    `/* eslint-disable */␊
+    /**␊
+     * This file was automatically generated by json-schema-to-typescript.␊
+     * DO NOT MODIFY IT BY HAND. Instead, modify the source JSONSchema file,␊
+     * and run json-schema-to-typescript to regenerate this file.␊
+     */␊
+    ␊
+    export interface ExactOptionalPropertyTypes {␊
+      maybe?: string | undefined;␊
+      complex?:␊
+        | {␊
+            maybe?: string | undefined;␊
+            [k: string]: Leaf;␊
+          }␊
+        | undefined;␊
+      [k: string]: string;␊
+    }␊
+    export interface Leaf {␊
+      maybe?: string | undefined;␊
+      [k: string]: unknown;␊
+    }␊
+    `
+
 ## options.format.js
 
 > Expected output to match snapshot for e2e test: options.format.js

test/__snapshots__/test/test.ts.md

@@ -0,0 +1,33 @@
+export const input = {
+  title: 'ExactOptionalPropertyTypes',
+  type: 'object',
+  properties: {
+    maybe: {
+      type: 'string',
+    },
+    complex: {
+      type: 'object',
+      properties: {
+        maybe: {
+          type: 'string',
+        },
+      },
+      additionalProperties: {
+        title: 'Leaf',
+        type: 'object',
+        properties: {
+          maybe: {
+            type: 'string',
+          },
+        },
+      },
+    },
+  },
+  additionalProperties: {
+    type: 'string',
+  }
+}
+
+export const options = {
+  exactOptionalPropertyTypes: true,
+}