Sequelize - Custom Operators

I'm interested in adding a couple custom operators to our usage of the Sequelize ORM. Specifically I want to add on operators that mimic the startswith and endswith lookup operators that Django has implemented. Looking through the internals on Sequelize, I can't seem to find the place where it would be to inject this kind of logic. In short, the functionality I'd like to implement is something like:

{
    stringField: {
        [Op.startsWith]: 'bl'
    }
}

to produce the desired sql of

WHERE stringField LIKE 'bl%'

I know that in the documentation all the examples show manually appending the % symbol but for my purposes I want to be able to dynamically wrap the value based on the operator being used.

You should be able to do this with the current version of sequelize,

Post.findAll(
  {
    where: {
      someAttribute: {
       $startsWith: 'my name' // or from the request body field value
     }
    }
  }
)

This can be found from the sequelize docs here for more operators. sequelize operators

Otherwise you can replace the $startsWith with the old version to suit your needs,

[Op.startsWith] : "field value"