FIx observable checking

Fixes #214

Author: sindresorhus

package.json

@@ -62,8 +62,8 @@
 		"jsdom": "^24.1.0",
 		"rxjs": "^7.8.1",
 		"tempy": "^3.1.0",
-		"tsimp": "^2.0.11",
-		"typescript": "^5.5.3",
+		"tsimp": "2.0.11",
+		"typescript": "5.5.3",
 		"xo": "^0.58.0",
 		"zen-observable": "^0.10.0"
 	},

source/index.ts

@@ -629,7 +629,7 @@ export function isObservable(value: unknown): value is ObservableLike {
 	}
 
 	// eslint-disable-next-line no-use-extend-native/no-use-extend-native, @typescript-eslint/no-unsafe-call
-	if (value === (value as any)[Symbol.observable]?.()) {
+	if (Symbol.observable !== undefined && value === (value as any)[Symbol.observable]?.()) {
 		return true;
 	}