Skip to content

tagged Sep 2, 2016 · 8451 commits to master since this release

Likely to cause new Flow errors:

  • If you check that an object obj has a property foo that Flow doesn't know about, Flow will now refine to the type mixed. If you then try to use in an unsafe way (like as a function), you might start seeing errors mentioning property foo of unknown type. The fix is to either fix the type of obj to include an optional property foo, or to rewrite code like && to typeof === "function" &&
  • We've fixed the type of Array.prototype.find to reflect the fact that it can return undefined
  • We've tightened up the checking of tuple types

New Features:

  • New syntax for exact object types: use {| and |} instead of { and }. Where {x: string} contains at least the property x, {| x: string |} contains ONLY the property x.
  • Flow now watches for .css, .jpg, .png, .gif, .eot, .svg, .ttf, .woff, .woff2, .mp4 and .webm files (this list is not configurable at the moment). We call them resource files. If you require a resource file, you get a string (except for .css files, for which you get an Object). You should still be able to use module.name_mapper to map a resource file to a mock, if you prefer.
  • We're starting work on flow gen-flow-files, which consumes Flow code and outputs .flow files containing only the types exported. It's alpha-level and we're still iterating on it, so use at your own peril!

Notable bug fixes:

  • Fixed a bug where, if a module has a CommonJS export of type any, then the types it exported were also given type any
  • v0.31.0 contained a regression where arrays and promises required more annotations than they should. This is fixed.
  • Fixed use of tagged unions with intersections and generics.
  • Jump to definition for overridden methods was jumping to the wrong method. This is now fixed.
  • flow coverage had a non-termination bug. This is now fixed.


  • Lots of improvements to the builtin libdefs! Thanks for all the pull requests!
Assets 5