option to prepend "readonly" to all fields

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 |
+| readonly | boolean | false | Generate all properties and array types as readonly. When true, all properties in interfaces will be prefixed with 'readonly', array types will be generated as 'readonly T[]', and index signatures will be readonly.
 | 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`.

src/generator.ts

@@ -157,6 +157,10 @@ function generateTypeUnmemoized(ast: AST, options: Options): string {
     return `${type} | undefined`
   }
 
+  if (options.readonly && ast.type === 'ARRAY') {
+    return `readonly ${type}`
+  }
+
   return type
 }
 export const generateType = memoize(generateTypeUnmemoized)
@@ -305,6 +309,7 @@ function generateInterface(ast: TInterface, options: Options): string {
       .map(
         ([isRequired, keyName, ast, type]) =>
           (hasComment(ast) && !ast.standaloneName ? generateComment(ast.comment, ast.deprecated) + '\n' : '') +
+          (options.readonly ? 'readonly ' : '') +
           escapeKeyName(keyName) +
           (isRequired ? '' : '?') +
           ': ' +

src/index.ts

@@ -52,6 +52,12 @@ export interface Options {
    * Create enums from JSON enums with eponymous keys
    */
   inferStringEnumKeysFromValues: boolean
+  /**
+   * Generate all properties and array types as readonly.
+   * When true, all properties in interfaces will be prefixed with 'readonly',
+   * array types will be generated as 'readonly T[]', and index signatures will be readonly.
+   */
+  readonly: 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,
+  readonly: false,
   format: true,
   ignoreMinAndMaxItems: false,
   maxItems: 20,

test/__snapshots__/test/test.ts.md

@@ -4,6 +4,28 @@ The actual snapshot is saved in `test.ts.snap`.
 
 Generated by [AVA](https://avajs.dev).
 
+## readonly.js
+
+> Expected output to match snapshot for e2e test: readonly.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 Readonly {␊
+      readonly user?: {␊
+        readonly name?: string;␊
+        readonly age?: number;␊
+        readonly hobbies?: readonly string[];␊
+        readonly [k: string]: unknown;␊
+      };␊
+      readonly [k: string]: unknown;␊
+    }␊
+    `
+
 ## JSONSchema.js
 
 > Expected output to match snapshot for e2e test: JSONSchema.js

test/e2e/readonly.ts

@@ -0,0 +1,31 @@
+export const input = {
+  $schema: 'http://json-schema.org/draft-07/schema',
+  type: 'object',
+  properties: {
+    user: {
+      type: 'object',
+      properties: {
+        name: {type: 'string'},
+        age: {type: 'number'},
+        hobbies: {
+          type: 'array',
+          items: {type: 'string'},
+        },
+      },
+    },
+  },
+}
+
+export const options = {
+  readonly: true,
+}
+
+export const output = `export interface User {
+  readonly name?: string;
+  readonly age?: number;
+  readonly hobbies?: readonly string[];
+}
+
+export interface Root {
+  readonly user?: User;
+}`