virtual()

Virtuals are properties that are added to the entities at runtime that are not persisted in the Datastore. You can both define a getter and a setter.

getter

const userSchema = new Schema({
    firstname: {},
    lastname : {}
});

userSchema.virtual('fullname').get(function fullName() {
    // the scope (this) is the entityData of the entity instance
    // for this reason don't use arrow functions here
    return `${this.firstname} ${this.lastname}`;
});

const User = gstore.model('User', schema);

const user = new User({ firstname:'John', lastname:'Snow' });
console.log(user.fullname); // 'John Snow';

/*
 * You can also set virtuals to true when calling plain() on your entity
 * to add them to the object returned.
 */
const response = user.plain({ virtuals: true });
console.log(response.fullname); // 'John Snow';

setter

const userSchema = new Schema({
    firstname: {},
    lastname : {}
});

userSchema.virtual('fullname').set(function(name) {
    const split = name.split(' ');
    this.firstname = split[0];
    this.lastname = split[1];
});

const User = gstore.model('User', schema);

const user = new User();
user.fullname = 'John Snow';

console.log(user.firstname); // 'John';
console.log(user.lastname); // 'Snow';

Note: You can save entities without worrying about the virtuals as they are removed from the entity data automatically.