How can we add String Validation Like Enum In Nodejs and Sequelize

 type: {
      type: DataTypes.STRING,
      defaultValue: "Normal"
    }

In this type I want to add validation only the type can be "Normal" or "Installment"

I don't want to use enum so how can I do custom validation in sequelize model?

You can add custom validations as mentioned in sequelize docs

You can try like:

type: {
  type: DataTypes.STRING,
  defaultValue: "Normal",
  validate: {
    isIn: [['Normal', 'Installment']]
  }

}

You can make the column an enum one if your enum values wont change.