Remove Symbol.observable polyfill

package.json

@@ -1,6 +1,6 @@
 {
   "name": "zen-observable",
-  "version": "0.9.0",
+  "version": "0.10.0",
   "repository": "zenparsing/zen-observable",
   "description": "An Implementation of ES Observables",
   "homepage": "https://github.com/zenparsing/zen-observable",

src/Observable.js

@@ -3,10 +3,6 @@
 const hasSymbol = name => Boolean(Symbol[name]);
 const getSymbol = name => hasSymbol(name) ? Symbol[name] : '@@' + name;
 
-if (!hasSymbol('observable') && Object.isExtensible(Symbol)) {
-  Symbol.observable = Symbol('observable');
-}
-
 const SymbolIterator = getSymbol('iterator');
 const SymbolObservable = getSymbol('observable');
 const SymbolSpecies = getSymbol('species');

test/from.js

@@ -41,14 +41,22 @@ describe('from', () => {
     it('wraps the input if it is not an instance of Observable', () => {
       let obj = {
         'constructor': Observable,
-        [Symbol.observable]() { return this },
+        [observableSymbol]() { return this },
+      };
+      assert.ok(Observable.from(obj) !== obj);
+    });
+
+    it('uses @@observable as the property name unless polyfilled', () => {
+      let obj = {
+        'constructor': Observable,
+        '@@observable'() { return this },
       };
       assert.ok(Observable.from(obj) !== obj);
     });
 
     it('throws if @@observable property is not a method', () => {
       assert.throws(() => Observable.from({
-        [Symbol.observable]: 1
+        [observableSymbol]: 1
       }));
     });
 
@@ -62,7 +70,7 @@ describe('from', () => {
       let observer;
       let cleanupCalled = true;
       let observable = Observable.from({
-        [Symbol.observable]() { return inner },
+        [observableSymbol]() { return inner },
       });
       observable.subscribe();
       assert.equal(typeof observer.next, 'function');

test/setup.js

@@ -4,6 +4,7 @@ beforeEach(() => {
   global.Observable = Observable;
   global.hostError = null;
   let $extensions = Object.getOwnPropertySymbols(Observable)[1];
-  let { hostReportError } = Observable[$extensions];
+  let { hostReportError, symbol } = Observable[$extensions];
   hostReportError.log = (e => global.hostError = e);
+  global.observableSymbol = symbol;
 });