fix(Symbol.iterator): correctly handle case where Symbol constructor …

…itself is not defined

spec/symbol/iterator-spec.ts

@@ -0,0 +1,33 @@
+import { expect } from 'chai';
+import * as sinon from 'sinon';
+import { root } from '../../src/internal/util/root';
+import { getSymbolIterator } from '../../src/internal/symbol/iterator';
+
+describe('iterator symbol', () => {
+  it('should use the real Symbol.iterator', () => {
+    const Symbol_iterator = getSymbolIterator(root);
+    expect(Symbol_iterator).to.equal(Symbol.iterator);
+  });
+
+  it('should use a fake @@iterator string as a symbol when it the real one does not exist', () => {
+    sinon.spy(console, 'warn');
+
+    const Symbol_iterator = getSymbolIterator({
+      Symbol: (() => {}) as SymbolConstructor // tslint:disable-line:no-empty
+    });
+    expect(Symbol_iterator).to.equal('@@iterator');
+    expect(console.warn).have.been.calledWithExactly('RxJS: Symbol.iterator does not exist, so things like from(iterable) won\'t work');
+
+    (console.warn as any).restore();
+  });
+
+  it('should use a fake @@iterator string as a symbol when Symbol is not even defined', () => {
+    sinon.spy(console, 'warn');
+
+    const Symbol_iterator = getSymbolIterator({});
+    expect(Symbol_iterator).to.equal('@@iterator');
+    expect(console.warn).have.been.calledWithExactly("RxJS: Symbol.iterator does not exist, so things like from(iterable) won't work");
+
+    (console.warn as any).restore();
+  });
+});

src/internal/symbol/iterator.ts

@@ -1,14 +1,19 @@
+import { root } from '../util/root';
 
-/* NOTE: Warning users that they don't have a Symbol.iterator
-   polyfill. We don't want to throw on this, because it's not required
-   by the library. However it will provide clues to users on older
-   browsers why things like `from(iterable)` doesn't work. */
-if (!Symbol || !Symbol.iterator) {
-  console.warn('RxJS: Symbol.observable does not exist');
+export function getSymbolIterator(root: { Symbol?: SymbolConstructor }): symbol {
+  /* NOTE: Warning users that they don't have a Symbol.iterator
+     polyfill. We don't want to throw on this, because it's not required
+     by the library. However it will provide clues to users on older
+     browsers why things like `from(iterable)` doesn't work. */
+  if (typeof root.Symbol !== 'function' || !root.Symbol.iterator) {
+    console.warn('RxJS: Symbol.iterator does not exist, so things like from(iterable) won\'t work');
+    return '@@iterator' as any;
+  }
+
+  return root.Symbol.iterator;
 }
 
-/** The native Symbol.iterator instance or a string */
-export const iterator = Symbol && Symbol.iterator || '@@iterator';
+export const iterator = getSymbolIterator(root);
 
 /**
  * @deprecated use {@link iterator} instead