typescript Symbol.iterator
It isn't a bug. It depends on your target.
TypeScript made a (terrible, in my opinion) design decision that if you transpile TS for..of to ES5 or ES3, it emits a normal for (var i; i < testingIterables.length; i++) loop.
For that reason, for targets ES5 and ES3, only arrays and strings are allowed in for..of loops.
There are several options to remedy this:
- If your TypeScript is over 2.3, you can set the
downlevelIterationflag to true, this will cause TypeScript to compile iterator correctly, but it means you must have a Symbol.iterator polyfill in runtime for non-supporting browsers, else you risk runtime errors in unexpected places for those browsers. - Select a higher target, ES2015 or higher would work. You can then transpile further down with the use of Babel (you'll also need a runtime polyfill to make Symbols work)
- Unwrap the iterator yourself with the use of
whileand calls totestingIterables.next().