From 844b43c9dfcc3caca36001e35466918d57136bcf Mon Sep 17 00:00:00 2001
From: Sindre Sorhus <sindresorhus@gmail.com>
Date: Thu, 13 Dec 2018 16:52:55 +0100
Subject: [PATCH] Improve the `is.observable` check (#74)

Fixes #72
---
 package.json         |  3 ---
 source/index.ts      | 18 ++++++++++++++++--
 source/tests/test.ts | 20 ++++++++++++--------
 3 files changed, 28 insertions(+), 13 deletions(-)

diff --git a/package.json b/package.json
index 40dd260..c7b2983 100644
--- a/package.json
+++ b/package.json
@@ -43,9 +43,6 @@
 		"verify",
 		"compare"
 	],
-	"dependencies": {
-		"symbol-observable": "^1.2.0"
-	},
 	"devDependencies": {
 		"@sindresorhus/tsconfig": "^0.1.0",
 		"@types/jsdom": "^11.12.0",
diff --git a/source/index.ts b/source/index.ts
index 31fdc6d..babe375 100644
--- a/source/index.ts
+++ b/source/index.ts
@@ -2,7 +2,6 @@
 /// <reference lib="es2017.sharedmemory"/>
 /// <reference lib="esnext.asynciterable"/>
 /// <reference lib="dom"/>
-import symbolObservable from 'symbol-observable';
 import {URL} from 'url';
 
 type TypedArray = Int8Array | Uint8Array | Uint8ClampedArray | Int16Array | Uint16Array | Int32Array | Uint32Array | Float32Array | Float64Array;
@@ -278,7 +277,22 @@ namespace is { // tslint:disable-line:no-namespace
 	export const domElement = (value: unknown): value is DomElement => object(value) && (value as DomElement).nodeType === NODE_TYPE_ELEMENT && string((value as DomElement).nodeName) &&
 		!plainObject(value) && DOM_PROPERTIES_TO_CHECK.every(property => property in (value as DomElement));
 
-	export const observable = (value: unknown) => Boolean(value && (value as any)[symbolObservable] && value === (value as any)[symbolObservable]());
+	export const observable = (value: unknown) => {
+		if (!value) {
+			return false;
+		}
+
+		if ((value as any)[Symbol.observable] && value === (value as any)[Symbol.observable]()) {
+			return true;
+		}
+
+		if ((value as any)['@@observable'] && value === (value as any)['@@observable']()) {
+			return true;
+		}
+
+		return false;
+	};
+
 	export const nodeStream = (value: unknown): value is NodeStream => !nullOrUndefined(value) && isObject(value) as unknown && function_((value as NodeStream).pipe) && !observable(value);
 
 	export const infinite = (value: unknown) => value === Infinity || value === -Infinity;
diff --git a/source/tests/test.ts b/source/tests/test.ts
index 15bc9bf..cc4353e 100644
--- a/source/tests/test.ts
+++ b/source/tests/test.ts
@@ -345,6 +345,14 @@ const types = new Map<string, Test>([
 			document.createDocumentFragment()
 		]
 	}],
+	['observable', {
+		is: is.observable,
+		fixtures: [
+			new Observable(),
+			new Subject(),
+			new ZenObservable(() => {}) // tslint:disable-line:no-empty
+		]
+	}],
 	['nodeStream', {
 		is: is.nodeStream,
 		fixtures: [
@@ -359,14 +367,6 @@ const types = new Map<string, Test>([
 			new Stream.Writable()
 		]
 	}],
-	['observable', {
-		is: is.observable,
-		fixtures: [
-			new Observable(),
-			new Subject(),
-			new ZenObservable(() => {})	// tslint:disable-line:no-empty
-		]
-	}],
 	['infinite', {
 		is: is.infinite,
 		fixtures: [
@@ -761,6 +761,10 @@ test('is.domElement', t => {
 	t.false(is.domElement({nodeType: 1, nodeName: 'div'}));
 });
 
+test('is.observable', t => {
+	testType(t, 'observable');
+});
+
 test('is.nodeStream', t => {
 	testType(t, 'nodeStream');
 });