Add parseJson option (#272)

* feat: Options.parseJson

fixes #254

* Update index.d.ts

* Update readme.md

* Support parseJson option with response.json()

* docs: remove the limitation clause

* Update index.js

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>
Co-authored-by: Seth Holladay <me@seth-holladay.com>

index.d.ts

@@ -206,6 +206,29 @@ export interface Options extends Omit<RequestInit, 'headers'> {
 	*/
 	json?: unknown;
 
+	/**
+	User-defined JSON-parsing function.
+
+	Use-cases:
+	1. Parse JSON via the [`bourne` package](https://github.com/hapijs/bourne) to protect from prototype pollution.
+	2. Parse JSON with [`reviver` option of `JSON.parse()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/parse).
+
+	@default JSON.parse()
+
+	@example
+	```
+	import ky from 'ky';
+	import bourne from '@hapijs/bourne';
+
+	(async () => {
+		const parsed = await ky('https://example.com', {
+			parseJson: text => bourne(text)
+		}).json();
+	})();
+	```
+	*/
+	parseJson?: (text: string) => unknown
+
 	/**
 	Search parameters to include in the request URL. Setting this will override all existing search parameters in the input URL.
 

index.js

@@ -328,6 +328,12 @@ class Ky {
 				return this._stream(response.clone(), this._options.onDownloadProgress);
 			}
 
+			if (this._options.parseJson) {
+				response.json = async () => {
+					return this._options.parseJson(await response.text());
+				};
+			}
+
 			return response;
 		};
 
@@ -337,8 +343,20 @@ class Ky {
 		for (const [type, mimeType] of Object.entries(responseTypes)) {
 			result[type] = async () => {
 				this.request.headers.set('accept', this.request.headers.get('accept') || mimeType);
+
 				const response = (await result).clone();
-				return (type === 'json' && response.status === 204) ? '' : response[type]();
+
+				if (type === 'json') {
+					if (response.status === 204) {
+						return '';
+					}
+
+					if (options.parseJson) {
+						return options.parseJson(await response.text());
+					}
+				}
+
+				return response[type]();
 			};
 		}
 

readme.md

@@ -346,6 +346,28 @@ import ky from 'ky';
 })();
 ```
 
+##### parseJson
+
+Type: `Function`\
+Default: `JSON.parse()`
+
+User-defined JSON-parsing function.
+
+Use-cases:
+1. Parse JSON via the [`bourne` package](https://github.com/hapijs/bourne) to protect from prototype pollution.
+2. Parse JSON with [`reviver` option of `JSON.parse()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/parse).
+
+```js
+import ky from 'ky';
+import bourne from '@hapijs/bourne';
+
+(async () => {
+	const parsed = await ky('https://example.com', {
+		parseJson: text => bourne(text)
+	}).json();
+})();
+```
+
 ### ky.extend(defaultOptions)
 
 Create a new `ky` instance with some defaults overridden with your own.

test/main.js

@@ -585,3 +585,50 @@ test('POST JSON with falsey value', async t => { // #222
 
 	await server.close();
 });
+
+test('parseJson option with response.json()', async t => {
+	const json = {hello: 'world'};
+
+	const server = await createTestServer();
+	server.get('/', async (request, response) => {
+		response.json(json);
+	});
+
+	const response = await ky.get(server.url, {
+		parseJson: text => ({
+			...JSON.parse(text),
+			extra: 'extraValue'
+		})
+	});
+	const responseJson = await response.json();
+
+	t.deepEqual(responseJson, {
+		...json,
+		extra: 'extraValue'
+	});
+
+	await server.close();
+});
+
+test('parseJson option with promise.json() shortcut', async t => {
+	const json = {hello: 'world'};
+
+	const server = await createTestServer();
+	server.get('/', async (request, response) => {
+		response.json(json);
+	});
+
+	const responseJson = await ky.get(server.url, {
+		parseJson: text => ({
+			...JSON.parse(text),
+			extra: 'extraValue'
+		})
+	}).json();
+
+	t.deepEqual(responseJson, {
+		...json,
+		extra: 'extraValue'
+	});
+
+	await server.close();
+});