index.js

var Sequelize = require('sequelize');

function JsonField(db, modelName, fieldName, options) {
  var self = this;
  options = options || {};

  process.nextTick(function() {
    db.models[modelName].hook('beforeValidate', function(instance) {
      if (typeof instance.dataValues[fieldName] != 'string') {
        instance.setDataValue(fieldName, JSON.stringify(instance.getDataValue(fieldName)));
        return self;
      } else if (instance.dataValues[fieldName] == 'null') {
        instance.setDataValue(fieldName, null);
      }
    });
  });

  return {
    type: options.type || Sequelize.TEXT,
    get: function() {
      var currentValue = this.getDataValue(fieldName);
      if (typeof currentValue == 'string') {
        this.dataValues[fieldName] = JSON.parse(currentValue);
      }
      return this.dataValues[fieldName];
    },
    set: function(value) {
      this.setDataValue(fieldName, JSON.stringify(value))
    }
  }
}

module.exports = JsonField;