fix: Better object checks

src/body.js

@@ -9,11 +9,12 @@ import Stream from 'stream';
 
 import Blob, {BUFFER} from './blob';
 import FetchError from './fetch-error';
+import {isBlob, isURLSearchParams} from './utils/is';
 
 let convert;
 try {
 	convert = require('encoding').convert;
-} catch (error) {}
+} catch (error) { }
 
 const INTERNALS = Symbol('Body internals');
 
@@ -341,47 +342,6 @@ function convertBody(buffer, headers) {
 	).toString();
 }
 
-/**
- * Detect a URLSearchParams object
- * ref: https://github.com/bitinn/node-fetch/issues/296#issuecomment-307598143
- *
- * @param   Object  obj     Object to detect by type or brand
- * @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';
-}
-
-/**
- * Check if `obj` is a W3C `Blob` object (which `File` inherits from)
- * @param  {*} obj
- * @return {boolean}
- */
-function isBlob(obj) {
-	return typeof obj === 'object' &&
-				typeof obj.arrayBuffer === 'function' &&
-				typeof obj.type === 'string' &&
-				typeof obj.stream === 'function' &&
-				typeof obj.constructor === 'function' &&
-				typeof obj.constructor.name === 'string' &&
-				/^(Blob|File)$/.test(obj.constructor.name) &&
-				/^(Blob|File)$/.test(obj[Symbol.toStringTag]);
-}
-
 /**
  * Clone body given Res/Req instance
  *

src/request.js

@@ -12,6 +12,7 @@ import Stream from 'stream';
 import utf8 from 'utf8';
 import Headers, {exportNodeCompatibleHeaders} from './headers';
 import Body, {clone, extractContentType, getTotalBytes} from './body';
+import {isAbortSignal} from './utils/is';
 
 const INTERNALS = Symbol('Request internals');
 
@@ -22,27 +23,18 @@ const formatUrl = Url.format;
 const streamDestructionSupported = 'destroy' in Stream.Readable.prototype;
 
 /**
- * Check if a value is an instance of Request.
+ * Check if `obj` is an instance of Request.
  *
- * @param   Mixed   input
- * @return  Boolean
+ * @param  {*} obj
+ * @return {boolean}
  */
-function isRequest(input) {
+function isRequest(obj) {
 	return (
-		typeof input === 'object' &&
-		typeof input[INTERNALS] === 'object'
+		typeof obj === 'object' &&
+		typeof obj[INTERNALS] === 'object'
 	);
 }
 
-function isAbortSignal(signal) {
-	const proto = (
-		signal &&
-		typeof signal === 'object' &&
-		Object.getPrototypeOf(signal)
-	);
-	return Boolean(proto && proto.constructor.name === 'AbortSignal');
-}
-
 /**
  * Request class
  *

src/utils/is.js

@@ -0,0 +1,60 @@
+/**
+ * Is.js
+ *
+ * Object type checks.
+ */
+
+const NAME = Symbol.toStringTag;
+
+/**
+ * Check if `obj` is a URLSearchParams object
+ * ref: https://github.com/bitinn/node-fetch/issues/296#issuecomment-307598143
+ *
+ * @param  {*} obj
+ * @return {boolean}
+ */
+export function isURLSearchParams(obj) {
+	return (
+		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' &&
+        typeof obj.sort === 'function' &&
+        obj[NAME] === 'URLSearchParams'
+	);
+}
+
+/**
+ * Check if `obj` is a W3C `Blob` object (which `File` inherits from)
+ *
+ * @param  {*} obj
+ * @return {boolean}
+ */
+export function isBlob(obj) {
+	return (
+		typeof obj === 'object' &&
+        typeof obj.arrayBuffer === 'function' &&
+        typeof obj.type === 'string' &&
+        typeof obj.stream === 'function' &&
+        typeof obj.constructor === 'function' &&
+        /^(Blob|File)$/.test(obj[NAME])
+	);
+}
+
+/**
+ * Check if `obj` is an instance of AbortSignal.
+ *
+ * @param  {*} obj
+ * @return {boolean}
+ */
+export function isAbortSignal(obj) {
+	return (
+		obj &&
+        typeof obj === 'object' &&
+        obj[NAME] === 'AbortSignal'
+	);
+}
+