Update client JS to ES6

[Paul-Guerra]

ES6 is the latest standard for the javascript language with a slew of new features and syntactic sugar. It is supported in Node 6+ and the browsers, of course, have varying levels of support.

Yes this is going to introduce more tooling. I'm not a fan but this is life on the front end.

You should

• Rewrite the 2 front end JS files in ES6
• Use Babel to compile the modern javascript into something supported in all browsers
• Create a build based on the code you wrote in ES6. There are multiple ways you can combine the ES6 build step into your bundle build step. Each will have their own pros and cons.