ES6 Class, pass function as parameter to register expressjs routes

Use bind method to bind the scope, like this

this.app.get(APISLUG + this.name, this.all.bind(this));

You can set an arrow function as a property on the class. Arrow functions lexically binds the this value (https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Functions/Arrow_functions).

In your example:

export default class BaseController {
  ...
  all = (req, res, next) => { // This is the only line that changed
    ...
  }
}

Note that arrow functions on classes are not standard ES6 syntax, but will probably come with ES7 (some notes about that in comments here: https://stackoverflow.com/a/31362350/2054731). You may need to configure your project to be able to use this and/or other ES7 features.