gistfile1.txt

const defaults = (obj, defaultProps) => {
  Object.keys(obj).forEach((key) => {
    if (obj[key] === undefined) obj[key] = defaultProps[key];
  });
};

const Foo = function() {
  const instance = {};
  defaults(instance, instanceMethods);
  instance.value = 0;
  return instance;
};

const instanceMethods = {
  bar: () => {
    instance.value++;
  }
};

const f = new Foo();
f.bar() // outputs "ReferenceError: instance is not defined [Learn More]". why?