ES6 this can't see the members f the class

Question

I have the following class

class Foo {
  baz = 42
  url = 'www.foo.bar'
  foo(){
    console.log('Hello from foo')
    return 'baz'
  }
  run() {
    let nightmare = Nightmare()
    var _this = this
    nightmare
      .on('console', (log, msg) => {
      console.log(msg)
      })
      .goto(this.url)
      .evaluate((ctx)=>{
        console.log('hello from evaluate')
        ctx.foo()
        return 'title'
      }, _this)
      .end()
      .then(function(title){
        console.log(title);
      })
  }
}

I try to divide up the scraping into methods, but I can't find out how to call a member from the evaluate function. I can only see

hello from evaluate

It looks like foo is never called.