mongoose-schema.js

const Account = new Schema({
  email: { 
    type: String,
    unique: true,
    lowercase: true
  },
  nickname:  {
    type: String,
    unique: true,
    lowercase: true
  },
  password: String,
  listings: [
    {
      itemOffered: String,
      itemSought: String,
      sellFor: Number,
      description: String,
      images: []
    }
  ]
});


let saveListingForm = { $push: { listings: { 
  "itemOffered": itemOffered,
  "itemSought": itemSought,
  "sellFor": sellFor,
  "description": description,
  "images": ???
 } } };