You are a skilled programmer who has a desire to work on the internal engine of a JavaScript virtual machine in a context that will impact real developers.

We are Moddable, makers of the open source XS JavaScript Engine and the Moddable SDK — tools and runtime software focused on software for microcontrollers.

Together we will spend the summer improving and extending the XS Engine.

This is a unique opportunity to work on a JavaScript engine of an approachable size and complexity. The implementation of XS is much easier to read, understand, and modify than engines that power modern browsers.

And yet, XS has considerable real-world impact: Moddable is helping shape the future of JavaScript for microcontrollers via its membership in Ecma TC39, the Moddable SDK is being used in a variety of enterprise solutions, and all of the code produced as part of this internship will be made available to the public.

The focus of this internship is improving the core functionality of XS. Your area of work for the summer is based on your interests and abilities. Examples of potential areas of work include, but are not limited to:

  • Performance optimization
  • Memory use optimization
  • Engine code size optimization
  • Byte code size optimization
  • Debugging
  • Performance profiling
  • API hardening
  • Dead stripping (e.g. removal of unused JavaScript functions)

Essential duties and responsibilities

  • Join the Moddable team for 12 to 16 weeks at our office in the heart of downtown Palo Alto, CA. We have convenient access to CalTrain, Highways 101 & 280, restaurants, and Stanford University.
  • Work directly with the creators of XS to improve the performance and reliability of the engine.
  • Participate in code reviews and architectural discussions.
  • Communicate your findings and work with the world via the Moddable blog and GitHub.


  • Considerable programming experience in C
  • Experience building interpreters
  • Knowledge of programming language theory
  • Excellent communication skills

To apply

If you are interested in joining us, please send your résumé/CV to along with a note describing why you believe you would be a good fit for the team. We’ll make a decision quickly –- we know that it’s getting late in the semester.

Moddable compensates interns commensurate with experience and education.