Sequelize OR condition object

By creating object like this

var condition=
{
  where:
  {
     LastName:"Doe"，
     FirstName:["John","Jane"],
     Age:{
       gt:18
     }
  }    
}

and pass it in

Student.findAll(condition)
.success(function(students){

})

It could beautifully generate SQL like this

"SELECT * FROM Student WHERE LastName='Doe' AND FirstName in ("John","Jane") AND Age>18"

However, It is all 'AND' condition, how could I generate 'OR' condition by creating a condition object?

Sequelize version 3 & 4 support the format below using $or, but this is not the latest version/latest format; see other answers which use symbols like [Sequelize.db.Op.or] etc introduced in Sequelize version 5:

where: {
    LastName: "Doe",
    $or: [
        {
            FirstName: 
            {
                $eq: "John"
            }
        }, 
        {
            FirstName: 
            {
                $eq: "Jane"
            }
        }, 
        {
            Age: 
            {
                $gt: 18
            }
        }
    ]
}

Will generate

WHERE LastName='Doe' AND (FirstName = 'John' OR FirstName = 'Jane' OR Age > 18)

See the doc: http://docs.sequelizejs.com/en/latest/docs/querying/#where