David Leong, Software Developer in Los Angeles, CA, United States
David Leong

Software Developer in Los Angeles, CA, United States

Member since October 23, 2017
David has twelve years of experience developing for the web primarily using React.js, Angular, and Vue.js for front-end and Django, Rails, Laravel, and Node.js for back-end programming. He also has a strong background in blockchain and ethereum technologies. David is especially good at producing quality code and embracing new technologies. He keeps abreast of technology trends always and adopts the best practice in development.
David is now available for hire



  • JavaScript, 10 years
  • Ruby, 8 years
  • Python, 8 years
  • Node.js, 8 years
  • Ruby on Rails (RoR), 6 years
  • Django, 6 years
  • React, 5 years
  • Angular, 3 years


Los Angeles, CA, United States



Preferred Environment

Mac OSX, VSCode, Git, SourceTree, Slack

The most amazing...

...thing I've built is the Slack-like text messaging web app using React.js backed by Rails based API.


  • Senior Web Engineer

    2018 - 2019
    Yuzu Solutions LLC (via Toptal)
    • Worked on developing educational simulation app based on simpl framework, simulation platform built with Python, Django, React.js, Redux, Crossbar & Autobahn.
    • Worked on building marketing simulation app based on simpl framework.
    • Worked on implementing business features.
    • Worked on re-skinning the app with new design.
    • Worked on upgrading React from v15 to v16.
    • Worked on implementing big tabular form using formik library.
    • Fixed npm packages vulnerabilities.
    • Took part in daily stand-up.
    Technologies: Python, Django, React, Redux
  • Full-Stack Web Engineer

    2018 - 2018
    PrepLink (via Toptal)
    • Worked as a full-stack engineer using Laravel and Vue.js frameworks.
    • Built back-end APIs for several features using Laravel best practice.
    • Implemented full-text search using Laravel Scout and Algolia.
    • Wrote many reusable Vue.js components using Vue.js best practice.
    • Improved old-fashioned Vue.js components that aren't written with modularity and DRY principles in mind.
    • Set up JavaScript code linting system using ESLint and Prettier.
    • Improved codebase file structure and utility and API request functions.
    • Contributed to bug-fixing and feature cards that span both front-end and back-end.
    Technologies: Laravel, Vue.js, HTML, SCSS, Bootstrap, ESLint
  • Full-Stack Web Engineer

    2018 - 2018
    Scoutible (via Toptal)
    • Improved outdated APIs written in Python.
    • Added some reusable base Python classes and defined some advanced patterns to improve the code design.
    • Improved front-end code quality using React.js and Redux-saga standard practice.
    • Upgraded outdated NPM packages.
    • Improved storing some app state info in local storage to persist to the browser.
    • Cleaned react components by using ESLint and defining prop types.
    • Contributed to bug-fixing and feature cards that span both front-end and back-end.
    Technologies: Python, JavaScript, React.js, Redux, Redux-saga, Google app engine, Google datastore
  • Senior Full-Stack Web Engineer

    2017 - 2018
    VolKno (via Toptal)
    • Wrote background working script that mines data and populates into database daily using Python.
    • Wrote utility scripts in Python.
    • Improved interacting with MySQL in Node.js using Sequelize ORM.
    • Improved outdated react-boilerplate codebase.
    • Implemented analytics charts using D3.js and Highcharts.js library.
    • Integrated video player.
    • Increased database performance by adding de-normalized fields and adding proper indices to tables.
    • Added new API endpoints in back-end by using best Express.js practice.
    Technologies: React.js, Redux, D3, Highcharts, Python, Node.js, Express.js, Sequelize, MySQL
  • Senior Full-Stack Web Developer

    2015 - 2017
    • Developed RESTful APIs for music/video commerce web app using Django-Rest-Framework.
    • Contributed to building APIs for recruiting CRM web app using Flask and SQLAlchemy.
    • Developed 5+ SPAs using React/Redux.
    • Developed GraphQL API using Node.js, Express.js and MongoDB.
    • Advocated interaction design best practices with a focus on consistency and usability.
    • Built reusable React.js and Vue.js components.
    • Reviewed the pull requests submitted from other front-end developers.
    • Improved live update of app state by using websocket channel events broadcast.
    • Collaborated with the design team to define data structure.
    • Provided consultation on functionality design and technologies to adopt.
    Technologies: React.js, Redux, Mobx, Angular, Vue.js, Ruby on Rails, Python, Django, Flask, Node.js
  • Senior Full-Stack Web Developer

    2012 - 2015
    • Built RESTful APIs using Flask and SQLAlchemy.
    • Wrote utility scripts in Python.
    • Integrated Webpack and React.js into Rails framework.
    • Collaborated with UI/UX team.
    • Ensured the technical feasibility of UI/UX designs.
    • Integrated and customized Material UI into AngularJS project.
    • Took part in making decisions on technologies to use.
    • Contributed to 3 Django applications.
    • Contributed to 3 Rails applications.
    • Reviewed the pull requests submitted from other developers.
    • Assured that code quality is above par using code linting tools.
    Technologies: Ruby on Rails, Sinatra, Python, Flask, Laravel, React.js, Vue.js, AngularJS, Webpack, Node.js, Python, Django, Flask
  • Full-Stack Web Developer

    2008 - 2012
    Waveguide LLC
    • Served as a full-stack developer using Python, PHP, HTML, CSS and Javascript.
    • Built RESTful APIs using Flask and SqlAlchemy.
    • Created semantic HTML pages.
    • Confirmed that all user input was validated before submitted to back-end.
    • Ensured software compliance with specified standards.
    • Contributed to deployment to hosting server.
    • Implemented page designs in standards-compliant dynamic XHTML and CSS.
    • Maintained reusable components repositories.
    • Researched new support technologies for development goals.
    Technologies: PHP, Laravel, Python, HTML, CSS, Javascript, Flask, sqlalchemy


  • Matching Therapeutics to Cancer Patients (Development)

    The MatchTx solution was built to utilize the proprietary algorithms for several different objectives and market segments.

    I was responsible for the doctors facing app, which predicts how well the patient will respond to a drug, or which treatment is best, based on characteristics and outcomes of the best-matched cohorts.

    The front-end is built in SPA using React.js.
    The backend provides RESTful APIs to the front-end app and is built with Django-rest-framework.

    Overall, my contributions were:
    - Built the front-end web app using React.js.
    - Implemented graph drawing using highchart.js.
    - Built RESTful APIs using Django rest framework.
    - Implemented the algorithm that predicts biopsy matching the patient using Kaplan Meier estimator.

  • Slack-like Text Messaging Web and Mobile App (Development)

    Text messaging web app for healthcare teams.

    It is a care coordination platform for healthcare teams, where patients and medical staff can interact.

    My contributions were:
    - Integrated Redux store management into React.js codebase.
    - Closely worked with back-end developers to optimize existing Web technology and create the best possible user experience.
    - Advocated Web interaction design best practices, with a focus on consistency and usability.
    - Built reusable React.js components.
    - Reviewed the pull requests submitted from other front-end developers.
    - Improved live update of the app state by proper handling of WebSocket channel events broadcast.
    - Collaborated with the design team to define the data structure.
    - Provided consultation on functionality design and technologies to adopt.

  • Sell Photography Online (Development)

    This project involved developing online photo storefront.

    Here is how it works:
    1. Set up and upload images
    2. Promote gallery
    3. Sell images
    4. Fulfill orders
    5. Get paid for orders

    As a front-end developer, I built the web app in SPA using Vue.js library.

    My responsibilities were:
    - Build a webpack hot-reload config and gulp tasks system
    - Manage web app store using vuex
    - Implement image uploading and cropping
    - Integrate payment system using Stripe
    - Build base CSS stylesheets


  • Languages

    PHP, ECMAScript (ES6), GraphQL, JavaScript, HTML, CSS, SCSS, SQL, Python, Ruby, TypeScript
  • Frameworks

    Laravel, Serverless Framework, Jest, Flux, Bootstrap 4, Bootstrap 3, Express.js, Flask, Django REST Framework, Vuetify.js, Angular Material, Protractor, Jasmine, Ruby on Rails (RoR), Redux, Django, Angular, Material-UI, AngularJS, Nuxt.js, Relay, OAuth 2
  • Libraries/APIs

    Ruby on Rails API, jQuery, Backbone.js, Vuex, Vue Material, React Router, React Redux, Devise, Redux Form, MobX, Pundit, Material 2, Socket.IO, Sidekiq, Reactstrap, Nokogiri, Flask-RESTful, Chai, SQLAlchemy, REST APIs, Nightwatch.js, Redux-saga, React, Node.js, Vue.js, Highcharts, Antd, Formik, API Development, D3.js, OmniAuth, RxJS, Facebook API
  • Tools

    Cucumber, Amazon Virtual Private Cloud (VPC), Bundler, AWS SES, Webpack, Pytest, RSpec, Angular CLI, Karma, Git, Capistrano, Mocha, Redux Thunk, VS Code, AWS ECS, RabbitMQ, Logstash, Auth0, AWS SDK, Kibana, Amazon SQS
  • Paradigms

    Functional Programming, Test-driven Development (TDD), Agile Software Development, Kanban, Behavior-driven Development (BDD), Scrum
  • Platforms

    MacOS, Red Hat Linux, Celery eCommerce, Heroku, AWS Lambda, Blockchain, Docker, Firebase, Ubuntu 16.04, Linux, Ubuntu 14.04, Ethereum
  • Storage

    PostgreSQL, AWS RDS, MySQL, Elasticsearch, MongoDB, Redis, AWS DynamoDB
  • Other

    Serverless, AWS API Gateway, Axios, Enzyme, Apollo, TSLint, ESLint, RESTful Web Services, GitFlow, Vue-router, Bootstrap UI, Front-end Development, eCommerce, Web Developer, React.js, Ruby on Rails, Bitcoin, Ethereum Smart Contracts


  • Bachelor's degree in Computer Science
    2005 - 2008
    California State University - Los Angeles, California, USA

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