Add optional ReadableStream polyfill

index.js

@@ -22,4 +22,10 @@ if (!global.AbortController) {
 	global.AbortController = AbortController;
 }
 
+if (!global.ReadableStream) {
+	try {
+		global.ReadableStream = require('web-streams-polyfill/ponyfill/es2018');
+	} catch (_) {}
+}
+
 module.exports = require('ky/umd');

package.json

@@ -62,7 +62,13 @@
 		"xo": "^0.25.3"
 	},
 	"peerDependencies": {
-		"ky": ">=0.17.0"
+		"ky": ">=0.17.0",
+		"web-streams-polyfill": ">=2.0.0"
+	},
+	"peerDependenciesMeta": {
+		"web-streams-polyfill": {
+			"optional": true
+		}
 	},
 	"browser": "browser.js",
 	"ava": {

readme.md

@@ -35,6 +35,28 @@ const ky = require('ky-universal');
 })();
 ```
 
+## `ReadableStream` support
+
+For [`ReadableStream`](https://developer.mozilla.org/en-US/docs/Web/API/ReadableStream) support, also install [`web-streams-polyfill`](https://github.com/MattiasBuelens/web-streams-polyfill):
+
+```
+$ npm install web-streams-polyfill
+```
+
+You can then use it normally:
+
+```js
+const ky = require('ky-universal');
+
+(async () => {
+	const {body} = await ky('https://httpbin.org/bytes/16');
+	const {value} = await body.getReader().read();
+	const result = new TextDecoder('utf-8').decode(value);
+
+	// …
+})();
+```
+
 ## API
 
 The API is exactly the same as the [Ky API](https://github.com/sindresorhus/ky#api).