title: Creating instance methods in a Sequelize Model using Typescript
body: <p>I want to extend a Sequelize Model class to add other instance methods but typescript keeps complaining that "Property 'prototype' does not exist on type 'Model'"</p>
  
  <pre><code>const MyModel = (sequelize: Sequelize.Sequelize, dataTypes: Sequelize.DataTypes) =&gt; {
    const User = sequelize.define&lt;Instance, Attribute&gt;(
      "users",
      {
        id: {
          type: dataTypes.INTEGER,
          primaryKey: true,
          autoIncrement: true,
        },
        email: {
          type: dataTypes.STRING
        },
        ...
      },
      {
        tableName: "users",
        ...
      },
    );
  
    User.prototype.verifyUser = function(password: string) {
      ...
    };
  
    return User;
  };
  </code></pre>
  
  <p>I expect <code>User.prototype.verifyUser</code> to work but typescript complains. How to add to typings?</p>