Appendix A. An overview of ECMAScript
At the time of writing, most web browsers fully support the ES6 specification, which introduced the most significant syntax additions. You can visit the ECMAScript compatibility site at http://mng.bz/ao59 to see the current state of ES6 support. Even if the users of your app have older browsers, you can develop in ES6/7/8 today and use transpilers like Traceur, Babel, or TypeScript to turn code that uses the latest syntax into its ES5 version.