Better compliance with Web IDL

- Make read-only attributes actually read-only
- Set @@toStringTag on the prototype only
- Make prototype methods/getters enumerable

Based on node-fetch#354.

Co-authored-by: Benjamin Seber <seber@synyx.de>

Author: TimothyGu

src/blob.js

@@ -6,13 +6,6 @@ const TYPE = Symbol('type');
 
 export default class Blob {
 	constructor() {
-		Object.defineProperty(this, Symbol.toStringTag, {
-			value: 'Blob',
-			writable: false,
-			enumerable: false,
-			configurable: true
-		});
-
 		this[TYPE] = '';
 
 		const blobParts = arguments[0];
@@ -87,8 +80,14 @@ export default class Blob {
 	}
 }
 
+Object.defineProperties(Blob.prototype, {
+	size: { enumerable: true },
+	type: { enumerable: true },
+	slice: { enumerable: true }
+});
+
 Object.defineProperty(Blob.prototype, Symbol.toStringTag, {
-	value: 'BlobPrototype',
+	value: 'Blob',
 	writable: false,
 	enumerable: false,
 	configurable: true

src/body.js

@@ -11,16 +11,15 @@ import FetchError from './fetch-error.js';
 const Stream = require('stream');
 const { PassThrough } = require('stream');
 
-const DISTURBED = Symbol('disturbed');
-const ERROR = Symbol('error');
-
 let convert;
 try { convert = require('encoding').convert; } catch(e) {}
 
+const INTERNALS = Symbol('Body internals');
+
 /**
- * Body class
+ * Body mixin
  *
- * Cannot use ES6 class because Body must be called with .call().
+ * Ref: https://fetch.spec.whatwg.org/#body
  *
  * @param   Stream  body  Readable stream
  * @param   Object  opts  Response options
@@ -48,22 +47,28 @@ export default function Body(body, {
 		// coerce to string
 		body = String(body);
 	}
-	this.body = body;
-	this[DISTURBED] = false;
-	this[ERROR] = null;
+	this[INTERNALS] = {
+		body,
+		disturbed: false,
+		error: null
+	};
 	this.size = size;
 	this.timeout = timeout;
 
-	if (this.body instanceof Stream) {
-		this.body.on('error', err => {
-			this[ERROR] = new FetchError(`Invalid response body while trying to fetch ${this.url}: ${err.message}`, 'system', err);
+	if (body instanceof Stream) {
+		body.on('error', err => {
+			this[INTERNALS].error = new FetchError(`Invalid response body while trying to fetch ${this.url}: ${err.message}`, 'system', err);
 		});
 	}
 }
 
 Body.prototype = {
+	get body() {
+		return this[INTERNALS].body;
+	},
+
 	get bodyUsed() {
-		return this[DISTURBED];
+		return this[INTERNALS].disturbed;
 	},
 
 	/**
@@ -139,6 +144,16 @@ Body.prototype = {
 
 };
 
+// In browsers, all properties are enumerable.
+Object.defineProperties(Body.prototype, {
+	body: { enumerable: true },
+	bodyUsed: { enumerable: true },
+	arrayBuffer: { enumerable: true },
+	blob: { enumerable: true },
+	json: { enumerable: true },
+	text: { enumerable: true }
+});
+
 Body.mixIn = function (proto) {
 	for (const name of Object.getOwnPropertyNames(Body.prototype)) {
 		// istanbul ignore else: future proof
@@ -150,19 +165,21 @@ Body.mixIn = function (proto) {
 };
 
 /**
- * Decode buffers into utf-8 string
+ * Consume and convert an entire Body to a Buffer.
+ *
+ * Ref: https://fetch.spec.whatwg.org/#concept-body-consume-body
  *
  * @return  Promise
  */
-function consumeBody(body) {
-	if (this[DISTURBED]) {
-		return Body.Promise.reject(new Error(`body used already for: ${this.url}`));
+function consumeBody() {
+	if (this[INTERNALS].disturbed) {
+		return Body.Promise.reject(new TypeError(`body used already for: ${this.url}`));
 	}
 
-	this[DISTURBED] = true;
+	this[INTERNALS].disturbed = true;
 
-	if (this[ERROR]) {
-		return Body.Promise.reject(this[ERROR]);
+	if (this[INTERNALS].error) {
+		return Body.Promise.reject(this[INTERNALS].error);
 	}
 
 	// body is null
@@ -309,21 +326,21 @@ function convertBody(buffer, headers) {
  * @return  String
  */
 function isURLSearchParams(obj) {
-    // Duck-typing as a necessary condition.
-    if (typeof obj !== 'object' ||
-        typeof obj.append !== 'function' ||
-        typeof obj.delete !== 'function' ||
-        typeof obj.get !== 'function' ||
-        typeof obj.getAll !== 'function' ||
-        typeof obj.has !== 'function' ||
-        typeof obj.set !== 'function') {
-        return false;
-    }
-
-    // Brand-checking and more duck-typing as optional condition.
-    return obj.constructor.name === 'URLSearchParams' ||
-        Object.prototype.toString.call(obj) === '[object URLSearchParams]' ||
-        typeof obj.sort === 'function';
+	// Duck-typing as a necessary condition.
+	if (typeof obj !== 'object' ||
+		typeof obj.append !== 'function' ||
+		typeof obj.delete !== 'function' ||
+		typeof obj.get !== 'function' ||
+		typeof obj.getAll !== 'function' ||
+		typeof obj.has !== 'function' ||
+		typeof obj.set !== 'function') {
+		return false;
+	}
+
+	// Brand-checking and more duck-typing as optional condition.
+	return obj.constructor.name === 'URLSearchParams' ||
+		Object.prototype.toString.call(obj) === '[object URLSearchParams]' ||
+		typeof obj.sort === 'function';
 }
 
 /**
@@ -350,7 +367,7 @@ export function clone(instance) {
 		body.pipe(p1);
 		body.pipe(p2);
 		// set instance body to teed body and return the other teed body
-		instance.body = p1;
+		instance[INTERNALS].body = p1;
 		body = p2;
 	}
 
@@ -362,7 +379,7 @@ export function clone(instance) {
  * specified in the specification:
  * https://fetch.spec.whatwg.org/#concept-bodyinit-extract
  *
- * This function assumes that instance.body is present and non-null.
+ * This function assumes that instance.body is present.
  *
  * @param   Mixed  instance  Response or Request instance
  */

src/headers.js

@@ -84,13 +84,6 @@ export default class Headers {
 		} else {
 			throw new TypeError('Provided initializer must be an object');
 		}
-
-		Object.defineProperty(this, Symbol.toStringTag, {
-			value: 'Headers',
-			writable: false,
-			enumerable: false,
-			configurable: true
-		});
 	}
 
 	/**
@@ -214,12 +207,24 @@ export default class Headers {
 Headers.prototype.entries = Headers.prototype[Symbol.iterator];
 
 Object.defineProperty(Headers.prototype, Symbol.toStringTag, {
-	value: 'HeadersPrototype',
+	value: 'Headers',
 	writable: false,
 	enumerable: false,
 	configurable: true
 });
 
+Object.defineProperties(Headers.prototype, {
+	get: { enumerable: true },
+	forEach: { enumerable: true },
+	set: { enumerable: true },
+	append: { enumerable: true },
+	has: { enumerable: true },
+	delete: { enumerable: true },
+	keys: { enumerable: true },
+	values: { enumerable: true },
+	entries: { enumerable: true }
+});
+
 function getHeaderPairs(headers, kind) {
 	const keys = Object.keys(headers[MAP]).sort();
 	return keys.map(

src/index.js

@@ -84,18 +84,25 @@ export default function fetch(url, opts) {
 					return;
 				}
 
+				// Create a new Request object.
+				const requestOpts = {
+					headers: new Headers(request.headers),
+					follow: request.follow,
+					counter: request.counter + 1,
+					agent: request.agent,
+					compress: request.compress,
+					method: request.method
+				};
+
 				// per fetch spec, for POST request with 301/302 response, or any request with 303 response, use GET when following redirect
 				if (res.statusCode === 303
 					|| ((res.statusCode === 301 || res.statusCode === 302) && request.method === 'POST'))
 				{
-					request.method = 'GET';
-					request.body = null;
-					request.headers.delete('content-length');
+					requestOpts.method = 'GET';
+					requestOpts.headers.delete('content-length');
 				}
 
-				request.counter++;
-
-				resolve(fetch(resolve_url(request.url, res.headers.location), request));
+				resolve(fetch(new Request(resolve_url(request.url, res.headers.location), requestOpts)));
 				return;
 			}