Add req res data warn

src/request.js

@@ -6,7 +6,7 @@
  * All spec algorithm step numbers are based on https://fetch.spec.whatwg.org/commit-snapshots/ae716822cb3a61843226cd090eefc6589446c1d2/.
  */
 
-import {format as formatUrl} from 'node:url';
+import {deprecate, format as formatUrl} from 'node:url';
 import Headers from './headers.js';
 import Body, {clone, extractContentType, getTotalBytes} from './body.js';
 import {isAbortSignal} from './utils/is.js';
@@ -30,6 +30,10 @@ const isRequest = object => {
 	);
 };
 
+const doBadDataWarn = deprecate(() => {},
+	'.data is not a valid RequestInit property, use .body instead',
+	'https://github.com/node-fetch/node-fetch/issues/1000 (request)');
+
 /**
  * Request class
  *
@@ -58,6 +62,10 @@ export default class Request extends Body {
 		let method = init.method || input.method || 'GET';
 		method = method.toUpperCase();
 
+		if ('data' in init) {
+			doBadDataWarn();
+		}
+
 		// eslint-disable-next-line no-eq-null, eqeqeq
 		if ((init.body != null || (isRequest(input) && input.body !== null)) &&
 			(method === 'GET' || method === 'HEAD')) {

src/response.js

@@ -7,6 +7,7 @@
 import Headers from './headers.js';
 import Body, {clone, extractContentType} from './body.js';
 import {isRedirect} from './utils/is-redirect.js';
+import {deprecate} from 'util';
 
 const INTERNALS = Symbol('Response internals');
 
@@ -137,5 +138,8 @@ Object.defineProperties(Response.prototype, {
 	redirected: {enumerable: true},
 	statusText: {enumerable: true},
 	headers: {enumerable: true},
-	clone: {enumerable: true}
+	clone: {enumerable: true},
+	data: {get: deprecate(() => {},
+		'.data is not a valid Response property, use .json(), .text(), .arrayBuffer(), or .body instead',
+		'https://github.com/node-fetch/node-fetch/issues/1000 (response)')}
 });

test/request.js

@@ -283,4 +283,19 @@ describe('Request', () => {
 			expect(result).to.equal('a=1');
 		});
 	});
+
+	it('should warn once when using .data (request)', () => new Promise(resolve => {
+		const listenerFunc = ev => {
+			process.off('warning', listenerFunc);
+			expect(ev.message).to.equal('.data is not a valid RequestInit property, use .body instead');
+			resolve();
+		};
+
+		process.on('warning', listenerFunc);
+
+		// eslint-disable-next-line no-new
+		new Request(base, {
+			data: ''
+		});
+	}));
 });

test/response.js

@@ -248,4 +248,17 @@ describe('Response', () => {
 		expect(res.status).to.equal(0);
 		expect(res.statusText).to.equal('');
 	});
+
+	it('should warn once when using .data (response)', () => new Promise(resolve => {
+		const listenerFunc = ev => {
+			process.off('warning', listenerFunc);
+			expect(ev.message).to.equal('.data is not a valid Response property, use .json(), .text(), .arrayBuffer(), or .body instead');
+			resolve();
+		};
+
+		process.on('warning', listenerFunc);
+
+		const response = new Response('a');
+		response.data;
+	}));
 });