How to check if you have written ES6 code?

http://jshint.com/ or http://www.jslint.com/ - will detect ES6 specific specifications by just adding your code in the console

Add it into the Babel repl and see if it changes:

https://babeljs.io/repl/

:-) Hope that helps

Other than that it might be best to setup es6 with babel using webpack, gulp, rollup etc

So that if you write es6 or es5 it will automatically get converted and you can learn some new features on the way while still supporting es5 only browsers