function EE(fn, context, once) {
  this.fn = fn;
  this.context = context;
  this.once = once || false;
}
Representation of a single event listener.

@param {Function} fn The listener function.
@param {*} context The context to invoke the listener with.
@param {Boolean} [once=false] Specify if the listener is a one-time listener.
@constructor
@private