ES6 Classes: Unexpected token in script?

In ES2015, when using the class syntax, you need to define instance variables either in the constructor or one of the methods (there is a proposal for the next iteration, ES2016, to allow for your syntax: ES Class Fields & Static Properties)

class Counter {    constructor() {        this.count = 0;        setInterval(function() {            this.tick();        }.bind(this), 1000);    }    tick() {        this.count++;        console.log(this.count);    }}var c = new Counter();

Check out the fiddle:

http://www.es6fiddle.net/ifjtvu5f/

3 years late so you probably figured it out, but I placed the count variable in the constructor

class Counter {    constructor(count = 0) {      this.count = count        setInterval(function() {            this.tick();        }.bind(this), 1000);    }    tick() {        this.count ++;        console.log(this.count);    }}let counter = new Counter;counter.tick()

gave it more control by calling the tick function

class Counter {    constructor(count = 0) {      this.count = count;    }    tick() {        let count = this.count;        setInterval(function() {         console.log(count++);        }, 1000);    }}let counter = new Counter;// counter.tick()

Perhaps it's the compiler issue. Check what version of Babel you're using.
In my case I missed the babel-preset-stage-0 dependency.