title: NodeJs Sequelize removing properties in toJSON method leads to removed value from model itself
body: <p>I have a SequelizeInstance object which I need to omit some values when I change it into a JSON but whenever I call <strong>delete</strong>, it deletes that value from the SequelizeInstance as well. Here is code below:</p>
  
  <pre><code>instanceMethods: {
          toJSON: function() {
              var values = this.get();
              delete values.password;
              delete values.salt;
              return values;
          }
      }
  </code></pre>
  
  <p>The issue I'm facing is that whenever I called toJSON(), the SequelizeInstance will have removed the values for password and salt. A possible solution I can do is to do a shallow copy of the object and return that instead. I'm wondering is there are other better ways to approach this issue.</p>