const mapper = require('mapper.js'); const user = { id: 12345, firstName: 'Peter', lastName: 'Parker', company: { name: 'Daily Bugle', position: 'Photographer' }, email: 'peter.parker@marvel.com', socialNetworks: { vk: 'https://vk.com/peter.parker', facebook: 'https://www.facebook.com/peter.parker' }, friends: [ { id: 12346, firstName: 'Mary Jane', lastName: 'Watson' }, { id: 12347, firstName: 'Harold', lastName: 'Osborn' } ] }; const userSchema = { // take field without any changes id: true, // or '=', // you can specify function and return custom value fullName: (fullName, user) => user.firstName + ' ' + user.lastName, // take "name" field from "company" object companyName: 'company.name', // or '=company.name' // you can work with embedded objects contacts: { // by default property path is relative to current object, // so if you want to get value from top-level object ("user" in example) use "quot; email: '$.email', // or '=$.email' // function takes 4 arguments: // - current value of property = user.contacts.facebook // - current object = user.contacts // - original object = user // - path as array = ['contacts', 'facebook'] facebook: (facebook, contacts, user, path) => user.socialNetworks.facebook, vk: '$.socialNetworks.vk' }, // for arrays use array with schema for item friends: [{ id: true, fullName: (fullName, friend) => friend.firstName + ' ' + friend.lastName }] }; const mappedUser = mapper(user, userSchema); // or mapper(userSchema)(user) console.log(mappedUser);