Before Flow 0.28, the implementation of union/intersection types had serious bugs and was the root cause of a lot of weird behaviors you may have run into with Flow in the past. These bugs have now been addressed in a diff landing in 0.28.
Yesterday we deployed Flow v0.21.0! As always, we’ve listed out the most interesting changes in the Changelog. However, since I’m on a plane and can’t sleep, I thought it might be fun to dive into a couple of the changes! Hope this blog post turns out interesting and legible!
If you’re writing JSX, it’s probably a mix of your own React Components and some intrinsics. For example, you might write
render() {
return <div><FluffyBunny name="Fifi" /></div>;
}
In this example, FluffyBunny is a React Component you wrote and div is a JSX intrinsic. Lower-cased JSX elements are assumed to be intrinsics by React and by Flow. Up until Flow v0.21.0, Flow ignored intrinsics and gave them the type any. This meant Flow let you set any property on JSX intrinsics. Flow v0.21.0 will, by default, do the same thing as v0.20.0, However now you can also configure Flow to properly type your JSX intrinsics!
Flow v0.19.0 was deployed today! It has a ton of changes, which the Changelog summarizes. The Changelog can be a little concise, though, so here are some longer explanations for some of the changes. Hope this helps!
Flow is opt-in by default (you add @flow to a file). However we noticed that sometimes people would add Flow annotations to files that were missing @flow. Often, these people didn’t notice that the file was being ignored by Flow. So we decided to stop allowing Flow syntax in non-Flow files. This is easily fixed by adding either @flow or @noflow to your file. The former will make the file a Flow file. The latter will tell Flow to completely ignore the file.
Files that end with .flow are now treated specially. They are the preferred provider of modules. That is if both foo.js and foo.js.flow exist, then when you write import Foo from './foo', Flow will use the type exported from foo.js.flow rather than foo.js.
We imagine two main ways people will use .flow files.
Flow 0.14.0 included support for generator functions. Generator functions provide a unique ability to JavaScript programs: the abilty to suspend and resume execution. This kind of control paves the way for async/await, an upcoming feature already supported by Flow.
Today we released Flow v0.17.0! The first thing you may notice is that we changed the way we display errors at the command line. The new errors look like this:
This should hopefully help our command line users understand many errors without having to refer to their source code. We’ll keep iterating on this format, so tell us what you like and what you don’t like! Thanks to @frantic for building this feature!
There are a whole bunch of other features and fixes in this release! Head on over to our Release for the full list!