Question: When defining associations, how does Sequelize consider options?

[ThirteenTempest]

As noted in the documentation, the following syntax is all valid:

// Option 1
Foo.hasOne(Bar, {
  foreignKey: 'myFooId'
});
Bar.belongsTo(Foo);

// Option 2
Foo.hasOne(Bar, {
  foreignKey: {
    name: 'myFooId'
  }
});
Bar.belongsTo(Foo);

// Option 3
Foo.hasOne(Bar);
Bar.belongsTo(Foo, {
  foreignKey: 'myFooId'
});

// Option 4
Foo.hasOne(Bar);
Bar.belongsTo(Foo, {
  foreignKey: {
    name: 'myFooId'
  }
});

This implies that you can create associations with options in both the has and the belongs calls, which subsequently implies that it is possible to call these associations with conflicting information, such as:

Foo.hasOne(Bar, {
  as: 'myFooId'
});
Bar.belongsTo(Foo, {
  as: 'differentFooId'
});

What exactly happens in this scenario, and more generally, how does the option consideration actually occur?