const obj = {
  value: 10,
  getValue() {
    return this.value;
  },
  getArrowValue: () => {
    return this.value;
  },
  getMixedValue() {
    const regular = function() { return this.value; };
    const arrow = () => this.value;
    
    return [regular(), arrow()];
  }
};

console.log(obj.getMixedValue());