David Xu, Software Developer in Denver, United States
David Xu

Software Developer in Denver, United States

Member since October 20, 2016
David has taken several mobile apps from ideation to millions of users worldwide as the CTO of WhereTo, Chief Architect of Castle Global, Inc and technical lead in other companies. He has been programming since he was nine and has won medals in various competitive programming competitions, from the Australian Informatics Olympiad to ACM-ICPC. David has invaluable experience in all technical areas, from architecture and design to engineering and DevOps.
David is now available for hire

Portfolio

  • WhereTo, Inc.
    React, ES7, Babel, Swift, Redis, PostgreSQL, Go, Scala, Rust, Node.js...
  • Overtime
    Node.js, Swift, Objective-C, JavaScript, TypeScript, TestFlight, Docker...
  • GovDocs, Inc
    JavaScript, SuiteScript 1, Software Architecture, Architecture...

Experience

Location

Denver, United States

Availability

Part-time

Preferred Environment

GitHub, Git, Visual Studio Code, MacOS, WebStorm

The most amazing...

...thing I've done was scale the Kiwi Q&A to 50 million users, all while building new features for the platform and fixing bugs.

Employment

  • Chief Technology Officer

    2017 - PRESENT
    WhereTo, Inc.
    • Acted as the CTO for WhereTo, a SaaS technology company that empowers the business traveler or manager to get the best travel deal, enhances their booking experience, and incentivizes their business travel.
    • Partnered with top Fortune 100 companies to solve their frustrations with traditional corporate booking tools by utilizing our proprietary algorithm to provide the most optimal choices of flights, hotels, and car rentals.
    • Oversaw all aspects of technology, infrastructure, and R&D at WhereTo.
    Technologies: React, ES7, Babel, Swift, Redis, PostgreSQL, Go, Scala, Rust, Node.js, Puppeteer, APIs, Android, iOS, React Native, Google Play Store, Mobile App Development, Mobile Development, App Store, Databases, Full-stack, HTML5, Python, CI/CD Pipelines, Technical Leadership, Kotlin, Android Studio, API Integration, HubSpot, Back-end Architecture, Back-end, Front-end, TypeScript, Twilio, Twilio API, Redux, REST APIs, JSON Web Tokens (JWT), OAuth, Flux, Azure, Responsive Web Apps, JSX, SQL, AWS Lambda, Amazon API Gateway, Java, Software Architecture, Architecture, Enterprise Architecture, Leadership, Web Scraping, Scraping, Maps, Dashboards, Stripe Connect, Amazon ECS (Amazon Elastic Container Service), Event-driven Programming, Linux, Team Leadership, CTO, PHP, AWS, NoSQL, GraphQL, API Development, REST, Artificial Intelligence (AI), TestFlight, PostGIS, GIS, Docker, Management, Cross-functional Team Leadership, Teamwork, Cloud Architecture, Google Cloud Platform (GCP), Application Architecture, Networking, Apollo, Next.js, AWS RDS, Jest, Data Visualization, Laravel, Estimations, DevOps, Web Development, Agile, Load Testing, Fintech, Mobile, React Redux, Travel & Leisure, Stored Procedure, SQL Stored Procedures, Site Reliability Engineering (SRE), JSON, WebSockets, QA Automation, Continuous Integration (CI), Webpack, Debugging, Spark, Express.js, Full-stack Development, Large-scale Projects, Authentication, Stripe API, Realm, React Native for Web, Monorepos, Concurrent Programming, RESTful APIs, RESTful Development, Agile Software Development, OpenAPI, Memory Leaks
  • Developer

    2017 - 2018
    Overtime
    • Helped build a video editor for the Overtime app to add effects.
    • Built a commenting system for the overtime mobile app.
    • Built a leaderboard system for the Overtime mobile app.
    Technologies: Node.js, Swift, Objective-C, JavaScript, TypeScript, TestFlight, Docker, Teamwork, Cloud Architecture, Application Architecture, Networking, Consulting, Estimations, Web Development, Load Testing, Mobile, JSON, WebSockets, Continuous Integration (CI), Linux, Debugging, Authentication, Realm, React Native for Web, Concurrent Programming, RESTful APIs, RESTful Development, Agile Software Development, Memory Leaks
  • Back-end Developer (SuiteScript)

    2017 - 2018
    GovDocs, Inc
    • Built a REST API on top of NetSuite to provide all sorts of information to customers.
    • Architected the build system to allow the use of typed JavaScript to build around SuiteScript faster.
    • Worked with the front-end engineer to implement the API and helped other back-end engineers get up to speed and build efficiently.
    Technologies: JavaScript, SuiteScript 1, Software Architecture, Architecture, Amazon ECS (Amazon Elastic Container Service), Event-driven Programming, NoSQL, API Development, REST, Teamwork, Cloud Architecture, Application Architecture, Networking, Consulting, Jest, Compilers, Code Generators, Estimations, DevOps, Agile, NetSuite, Stored Procedure, SQL Stored Procedures, JSON, QA Automation, Continuous Integration (CI), Webpack, Debugging, Full-stack Development, Large-scale Projects, Authentication, Monorepos, Concurrent Programming, RESTful APIs, RESTful Development, Agile Software Development, OpenAPI, Memory Leaks
  • Chief Technology Officer

    2016 - 2018
    FlipTix, Inc
    • Managed and was responsible for all technical development, infrastructure, management, and R&D.
    • Architected the entire app with its back end.
    • Built the server in Node.js and deployed it on AWS.
    • Wrote the initial code for the iOS app in Swift.
    • Built the entire microservice architecture and architected all protocols.
    Technologies: React, ES7, Babel, Java, Swift, Redis, PostgreSQL, Go, Scala, Rust, Node.js, APIs, Android, iOS, Google Play Store, Mobile App Development, Mobile Development, App Store, Databases, Full-stack, HTML5, Python, CI/CD Pipelines, Technical Leadership, Kotlin, Android Studio, API Integration, Back-end Architecture, Back-end, Front-end, TypeScript, Twilio, Twilio API, Redux, REST APIs, JSON Web Tokens (JWT), OAuth, Responsive Web Apps, JSX, SQL, Software Architecture, Architecture, Enterprise Architecture, Leadership, Web Scraping, Scraping, Maps, Dashboards, Amazon ECS (Amazon Elastic Container Service), Event-driven Programming, Linux, Team Leadership, CTO, NoSQL, GraphQL, API Development, REST, PostGIS, GIS, Docker, Management, Cross-functional Team Leadership, Teamwork, Cloud Architecture, Google Cloud Platform (GCP), Application Architecture, Networking, Apollo, AWS RDS, Jest, Data Visualization, Estimations, DevOps, Marketplaces, Web Development, Agile, Load Testing, Mobile, React Redux, SQL Stored Procedures, Site Reliability Engineering (SRE), JSON, WebSockets, Continuous Integration (CI), Webpack, Debugging, Authentication, Stripe, Stripe API, React Native for Web, Concurrent Programming, RESTful APIs, RESTful Development, Agile Software Development, Memory Leaks
  • iOS Developer

    2016 - 2017
    SiteLite
    • Built extra features for the SiteLite app, an app allowing users to position and preview lights.
    • Implemented APIs and the UI using UIKit and AFNetworking.
    • Fixed a lot of bugs left over from the previous developer.
    Technologies: Swift, iOS, Image Processing, Software Architecture, Architecture, Event-driven Programming, REST, TestFlight, Teamwork, Application Architecture, Networking, Consulting, Estimations, Mobile, JSON, Debugging, Authentication, Concurrent Programming, RESTful APIs, RESTful Development, Agile Software Development
  • Full-stack Android Developer

    2016 - 2017
    MudFlap App
    • Built an MVP of the Mudflap app, an app that shows vital information to truckers on a map.
    • Worked with the front-end engineer to implement APIs I developed. Scraped a lot of information from various sources and merged them to create a giant database of POIs (Points of Interest).
    • Worked with the product and design team to implement an MVP for the Mudflap Android app.
    Technologies: Android, Software Architecture, Architecture, Web Scraping, Scraping, Maps, Dashboards, Event-driven Programming, Linux, Team Leadership, NoSQL, GraphQL, API Development, REST, PostGIS, GIS, Docker, Cross-functional Team Leadership, Teamwork, Cloud Architecture, Application Architecture, Networking, AWS RDS, Consulting, Estimations, DevOps, Web Development, Agile, Load Testing, Mobile, React Redux, Stored Procedure, SQL Stored Procedures, Site Reliability Engineering (SRE), JSON, WebSockets, Continuous Integration (CI), Webpack, Debugging, Express.js, Full-stack Development, Authentication, React Native for Web, Concurrent Programming, RESTful APIs, RESTful Development, Agile Software Development, OpenAPI
  • Chief Architect

    2015 - 2016
    Hive AI, Inc. (previously Castle Global, Inc.)
    • Built the commenting system for Kiwi using Node.js, PostgreSQL, and Redis.
    • Developed the AMA (Ask Me Anything) system for Kiwi, using Node.js, PostgreSQL, and Redis.
    • Led the development of Plaza's website, Plaza.tl.
    • Managed and led the back-end team for Kiwi's site. Kiwi.qa.
    • Extended the functionality of the moderation system I built previously; worked with data science team to add machine learning for automated pornographic, violent, and medical content detection.
    • Architected and built the version 2 of Kiwi's REST API.
    • Built the Chatous spam detection system using Golang and Redis.
    • Created the public questions feature for Kiwi using Node.js, PostgreSQL, and Redis.
    • Developed the topics feature for Kiwi (used Node.js, PostgreSQL, and Redis).
    • Rearchitected the feed, enabling more than one type of feed element to be displayed, and allowing feeds to be filtered (used Node.js, PostgreSQL, and Redis).
    • Developed the media questions feature for Kiwi, enabling rich media questions (used Node.js, PostgreSQL, Redis, and AWS S3).
    • Built the question curation (moderation) back-end for Kiwi, helping keep spammy questions off the site (used Node.js, PostgreSQL, Redis, React, Webpack, and Babel).
    • Made the moderation module for Plaza, preventing pornographic, violent, and medical content from being posted on the marketplace (used Node.js, PostgreSQL, Redis, React, Webpack, and Babel).
    • Integrated Plaza with email, enabling email based marketing to function (used Haraka and Node.js).
    • Built the mutual friends count feature for Plaza, enabling safer transactions (used Node.js, PostgreSQL, and Redis).
    • Rewrote the notifications system for Kiwi, adding new types of notifications for user engagement (used Node.js, Redis, and Google ProtoBuf).
    • Built the follower recommendation system for Kiwi (used Cassandra, Redis, Scala, and MySQL).
    • Set up the Jenkins integration for the CI pipeline.
    Technologies: Amazon Web Services (AWS), Go, AWS, Cassandra, Redis, RabbitMQ, Apache Kafka, MySQL, PostgreSQL, React, C++, Scala, Node.js, APIs, Android, iOS, React Native, Google Play Store, Mobile App Development, Mobile Development, App Store, Databases, Full-stack, HTML5, Python, CI/CD Pipelines, Technical Leadership, Android Studio, API Integration, Back-end Architecture, Back-end, Front-end, TypeScript, Jenkins, Twilio, Twilio API, Redux, JSON Web Tokens (JWT), OAuth, Responsive Web Apps, JSX, SQL, Java, Software Architecture, Architecture, Enterprise Architecture, Leadership, Web Scraping, Scraping, Maps, Dashboards, Stripe Connect, MongoDB, Event-driven Programming, Linux, Team Leadership, CTO, NoSQL, Dating Apps, GraphQL, API Development, REST, Artificial Intelligence (AI), TestFlight, PostGIS, GIS, Docker, Management, Cross-functional Team Leadership, Teamwork, Cloud Architecture, Application Architecture, Networking, Apollo, AWS RDS, Jest, Data Visualization, Compilers, Code Generators, Estimations, DevOps, Marketplaces, Web Development, Agile, Load Testing, Mobile, React Redux, Stored Procedure, Site Reliability Engineering (SRE), JSON, QA Automation, Continuous Integration (CI), Webpack, Debugging, Spark, Express.js, Full-stack Development, Large-scale Projects, Authentication, Stripe, Stripe API, Realm, React Native for Web, Monorepos, Concurrent Programming, RESTful APIs, RESTful Development, Agile Software Development, OpenAPI, Memory Leaks
  • Back-end Engineer

    2015 - 2015
    Castle Global, Inc. (previously Chatous, Inc.)
    • Built the moderation system, keeping pornographic, violent, and medical content off the service.
    • Developed the analytics system, handling more than 500 million data points daily.
    • Built the spatial search database server, powering nearby posts.
    • Created the entire back end and initial front end for Plaza.tl.
    • Introduced integration tests to Kiwi.
    • Scaled Kiwi from five million users to more than 55 million users.
    • Created various server monitoring tools.
    • Rewrote the photo resizer in Go and made it 10x faster.
    Technologies: Amazon Web Services (AWS), Go, AWS, Cassandra, Redis, RabbitMQ, Apache Kafka, MySQL, PostgreSQL, React, C++, Scala, Node.js, APIs, Android, iOS, Google Play Store, Mobile App Development, Mobile Development, App Store, Databases, Full-stack, HTML5, Python, CI/CD Pipelines, Android Studio, API Integration, Back-end Architecture, Back-end, TypeScript, Jenkins, Twilio, Twilio API, REST APIs, JSON Web Tokens (JWT), OAuth, SQL, Java, Software Architecture, Architecture, Web Scraping, Scraping, Dashboards, Stripe Connect, MongoDB, Event-driven Programming, Linux, NoSQL, Dating Apps, API Development, REST, Artificial Intelligence (AI), TestFlight, PostGIS, GIS, Docker, Teamwork, Cloud Architecture, Application Architecture, Networking, AWS RDS, Code Generators, Estimations, DevOps, Marketplaces, Web Development, Agile, Load Testing, Mobile, React Redux, Stored Procedure, SQL Stored Procedures, Site Reliability Engineering (SRE), JSON, WebSockets, QA Automation, Continuous Integration (CI), Webpack, Debugging, Spark, Express.js, Full-stack Development, Large-scale Projects, Authentication, Stripe, Stripe API, React Native for Web, Monorepos, Concurrent Programming, RESTful APIs, RESTful Development, Agile Software Development, OpenAPI, Memory Leaks
  • Founder | CEO | CTO

    2014 - 2015
    Aura Labs Pty Ltd
    • Built Aura, a proximity-based social network used to discover what's happening around you.
    • Developed iOS and Android apps.
    • Built the back-end server and deployed it on AWS using Elastic Beanstalk.
    Technologies: Java, Objective-C, Node.js, Amazon Web Services (AWS), MySQL, Redis, PHP, APIs, Android, iOS, Google Play Store, Mobile App Development, Mobile Development, App Store, Databases, Back-end Architecture, Back-end, Front-end, REST APIs, SQL, Architecture, API Development, REST, Teamwork, Application Architecture, Networking, Laravel, Web Development, Mobile, JSON, Debugging, Concurrent Programming, RESTful Development, Agile Software Development
  • iOS Engineer

    2013 - 2013
    BlondGorilla Pty Ltd
    • Built the mobile app, Danny Green's Fighting Fit, which was an app developed for Danny Green. It was used to instruct people on how to become good at fighting through streaming video and social integration.
    • Integrated Facebook and Twitter.
    • Developed the embedded video player.
    • Built the serialization mechanism for feeds.
    • Worked with a designer to implement the app.
    Technologies: Core Location, mediakit, OpenGL ES, UIKit, Core Graphics, Facebook API, Twitter API, SQLite, Objective-C, APIs, iOS, Mobile App Development, Mobile Development, App Store, Databases, API Integration, Back-end Architecture, Back-end, Front-end, REST APIs, SQL, Architecture, REST, Teamwork, Application Architecture, Agile, Mobile, JSON, Debugging, Concurrent Programming, RESTful Development, Agile Software Development
  • Mobile Engineer

    2013 - 2013
    Theme Solutions Pty Ltd
    • Developed Shareability, an app used to help parents connect with their children's schools.
    • Built and white-labeled the app for over 20 schools.
    • Created custom features as requested by schools.
    • Published more than 20 apps to the App Store and Google Play.
    Technologies: Urban Airship, PHP, Java, Objective-C, APIs, Android, iOS, Google Play Store, Mobile App Development, Mobile Development, App Store, Databases, API Integration, Back-end Architecture, Back-end, Front-end, REST APIs, SQL, Architecture, API Development, REST, Teamwork, Application Architecture, Agile, Mobile, JSON, Debugging, RESTful Development, Agile Software Development
  • Lead Engineer

    2012 - 2012
    Holobyte Pty Ltd
    • Worked as the lead developer of a mobile game for iPhone and iPad called Droodl.
    • Developed the app in Objective-C, using Cocos2D.
    • Built the back-end using PHP, deployed on AWS using Elastic Beanstalk.
    • Developed the custom OpenGL-ES renderer to render drawings.
    • Integrated everything with DynamoDB.
    Technologies: AWS, Amazon EC2 (Amazon Elastic Compute Cloud), Amazon DynamoDB, Amazon Web Services (AWS), Core Graphics, Cocos2d, UIKit, OpenGL ES, XML, JSON, Lua, PHP, Objective-C, APIs, Android, iOS, Mobile App Development, Mobile Development, App Store, Databases, API Integration, Back-end Architecture, Back-end, Front-end, REST APIs, SQL, Architecture, Linux, NoSQL, API Development, REST, Teamwork, Application Architecture, Web Development, Agile, Mobile, Debugging, Concurrent Programming, RESTful Development, Agile Software Development
  • Developer

    2011 - 2012
    CREFCO (via an Online Freelance Agency)
    • Developed the system for automatic credit pulls.
    • Built the outlook integration for credit checking.
    • Deployed it on Windows Server (in house).
    • Developed the automated emailing system for credit checks.
    Technologies: MySQL, PHP, C#, APIs, REST APIs, SQL, API Development, REST, Teamwork, Application Architecture, Web Development, Agile, Debugging
  • Web Developer

    2010 - 2011
    TrimEla (via an Online Freelance Agency)
    • Built the eCommerce platform for TrimEla, an online retailer for fashion goods.
    • Wrote website code using jQuery, CSS, and HTML.
    • Optimized the PHP back-end code.
    • Added features for international purchasers.
    • Built coupon features and implemented them.
    Technologies: HTML, CSS, JavaScript, PHP, APIs, REST APIs, SQL, REST, Teamwork, Application Architecture, Web Development, Agile, Debugging

Experience

  • Kiwi | Q&A

    Kiwi is a question and answer community of people who are curious to ask and eager to answer. We are a San Francisco-based startup with a new office in New Delhi, India. Since our launch in April 2015, more than 40 million unique users have joined Kiwi; we recently claimed the first spot on Apple App Store ahead of Facebook, YouTube, and Instagram.

  • Plaza

    Plaza is a local marketplace for people to buy and sell with their community.

  • Chatous
    https://chatous.com

    Chatous is a messaging app where you can talk anonymously with people from all over the world. Discuss shared interests or freely chat.

  • Gold | Australian Informatics Olympiad 2010

    Competed in and won a gold medal in AIO 2010.

  • Bronze | ACM-ICPC Regional 2011

    Competed in and won the bronze medal with my team in the ACM-ICPC Regional 2011 competition.

  • Renoria
    https://www.youtube.com/user/RenoriaDev

    Renoria was a MMORPG (Massively Multiplayer Online Role Playing Game) that I built when I was 13 years old. Built it in Java and C++, using LWJGL.

  • Melon
    https://www.businesstravelnews.com/Management/In-Ripe-SME-Market-Corporate-Traveler-Rolls-Out-Melon

    When it comes to business travel, you can have it all. Simpler bookings, unified systems, better user experience, convenience, tracking, 24/7 support, flexibility, savings, speed, and more. Corporate Traveler combined everything you need into one seamless travel experience. Melon, one platform powered by travel experts.

  • Vital Concepts for Modern JS Developers (Publication)
    This resource contains a collection of modern, vital JavaScript concepts provided by our Toptal network members.
  • Immutability in JavaScript Using Redux (Publication)
    In an ever growing ecosystem of rich and complicated JavaScript applications, there’s more state to be managed than ever before: the current user, the list of posts loaded, etc.Managing state can be hard and error prone, but immutability and Redux- a predictable state container for JavaScript apps- can help significantly. In this article, Toptal Programmer David Xu talks about managing state using immutability with Redux, a predictable state container.
  • Toptal Mentor
    David is a mentor in the Toptal Global Mentor’s Program. This program is a partnership between Toptal and General Assembly to provide high quality mentorship for students from minority and low income backgrounds who are looking to begin their careers as professional software engineers. David shows commitment to diversity in tech by mentoring a General Assembly student every week for a year, covering everything from coding tips and tricks to advice on making it in the industry.

Skills

  • Languages

    PHP, C, Objective-C, SQL, ES7, Java, CSS, HTML, JavaScript, HTML5, TypeScript, GraphQL, Stored Procedure, Go, Swift, Python, Kotlin, Scala, Lua, C#, C++, XML, Rust, SuiteScript 1
  • Frameworks

    Laravel, Express.js, Koa, Redux, React Native, JSON Web Tokens (JWT), Jest, Flux, Next.js, UIKit, Core Location, Cocos2d, Spark
  • Libraries/APIs

    React, jQuery, Node.js, REST APIs, API Development, React Redux, React Native for Web, Stripe, Google API, Twitter API, Facebook API, RxSwift, Puppeteer, Twilio API, Stripe Connect, Stripe API, OpenAPI, Core Graphics, OpenGL ES, TensorFlow, FlightAware XML3 Data APIs, GitHub API
  • Tools

    Git, GitHub, JSX, TestFlight, GIS, Webpack, RabbitMQ, Android Studio, Amazon ECS (Amazon Elastic Container Service), Sublime Text, Atom, Babel, PostCSS, Jenkins, WebStorm, CircleCI
  • Paradigms

    Model View Viewmodel (MVVM), Model View Controller (MVC), Object-oriented Programming (OOP), Concurrent Programming, Mobile Development, Back-end Architecture, Event-driven Programming, REST, Management, Application Architecture, DevOps, Agile, Load Testing, Continuous Integration (CI), RESTful Development, Agile Software Development, Functional Programming
  • Platforms

    Amazon Web Services (AWS), Linux, Docker, Android, iOS, Amazon EC2 (Amazon Elastic Compute Cloud), Apache Kafka, Azure, Google Cloud Platform (GCP), Mobile, Amazon Linux, Ubuntu, Twilio, AWS Lambda, MacOS, Visual Studio Code
  • Storage

    JSON, Amazon S3 (AWS S3), Redis, PostgreSQL, MySQL, Databases, NoSQL, PostGIS, SQL Stored Procedures, MongoDB, Realm, SQLite, Amazon DynamoDB, HBase, Cassandra
  • Industry Expertise

    Travel & Leisure
  • Other

    AWS, Ajax, Software Development, Front-end Development, Mixed Reality (MR), Freelance, APIs, Google Play Store, Mobile App Development, App Store, Full-stack, CI/CD Pipelines, Technical Leadership, API Integration, Back-end, Front-end, OAuth, Responsive Web Apps, Software Architecture, Architecture, Enterprise Architecture, Leadership, Web Scraping, Scraping, Maps, Dashboards, Team Leadership, CTO, Artificial Intelligence (AI), RESTful APIs, Cross-functional Team Leadership, Teamwork, Cloud Architecture, Networking, Apollo, AWS RDS, Consulting, Data Visualization, Compilers, Code Generators, Estimations, Marketplaces, Web Development, Site Reliability Engineering (SRE), WebSockets, QA Automation, Debugging, Full-stack Development, Large-scale Projects, Authentication, Monorepos, Memory Leaks, PayPal, RHEL, Google V8, Amazon Route 53, HAProxy, Amazon API Gateway, Dating Apps, Fintech, NetSuite, Urban Airship, mediakit, HubSpot, Image Processing, Travelport, Sabre, Hotels & Lodging, Machine Learning, SOAP

Education

  • Incomplete Bachelor's Degree in Computer Science
    2012 - 2013
    University of Western Australia - Perth, Western Australia

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