We chose TypeScript at Codecov when undergoing a recent rewrite of a legacy front end. Our previous front end was a mishmash of vanilla JavaScript and CoffeeScript , and was expanded upon haphazardly as the need arose. Without a unifying set of paradigms and patterns, the CoffeeScript and JavaScript setup was proving hard to maintain and expand upon by an engineering team. During a move to Vue.js , we decided to also make the move to TypeScript. Integrating TypeScript and Vue.js is fairly well understood at this point, so the setup wasn't all that difficult, and we felt that the benefits of incorporating TypeScript would outweigh the required time to set it up and get our engineering team up to speed.

Choosing to add TypeScript has given us one more layer to rely on to help enforce code quality, good standards, and best practices within our engineering organization. One of the biggest benefits for us as an engineering team has been how well our IDEs and editors (e.g., Visual Studio Code ) integrate with and understand TypeScript . This allows developers to catch many more errors at development time instead of relying on run time. The end result is safer (from a type perspective) code and a more efficient coding experience that helps to catch and remove errors with less developer effort.

I use TypeScript for Web Applications and for both frontend and backend because it has a lot of tooling around it and they really got the types and type safety right. Flow (JS) on the other hand lacks tooling and most of the times I scramble to find the right way of building my contracts in which TypeScript is very intuitive and natural. Additionally TypeScript is very similar to Java so your backend engineers and full stack engineers can work with it without much of context switch.

The only time I think Flow shines is (based on probably my outdated knowledge) Flow is/was the only option if you want/wanted to build a React Native application mainly because React Native transpiler at the time I was working with it would only work with flow.

I use TypeScript because it isn't just about validating the types I'm expecting to receive though that is a huge part of it too. Flow (JS) seems to be a type system only. TypeScript also allows you to use the latest features of JavaScript while also providing the type checking. To be fair to Flow (JS), I have not used it, but likely wouldn't have due to the additional features I get from TypeScript.

We originally (in 2017) started rewriting our platform from JavaScript to Flow (JS) but found the library support for Flow was lacking. After switching gears to TypeScript we've never looked back. At this point we're finding that frontend and backend libraries are supporting TypeScript out of the box and where the support is missing that the commuity is typically got a solution in hand.

I use TypeScript because the tooling is more mature (the decision to discontinue TSLint in favor of moving all its checks to ESLint is a thoughtful and mature decision), there's a ton of examples and tutorials for it, and it just generally seems to be where the industry is headed. Flow (JS) is a fine tool, but it just hasn't seen the uptake that TS has, and as a result is lacking a lot of the nicer small things, like thorough Visual Studio Code integration, offered by TS.

We currently use TypeScript at work. Previously we used Flow (JS) but it was sometimes really difficult to make the types work the way you want. Especially non-trivial types were problematic. And the IDE support wasn't good, Flow took too much resources and sometimes remain stuck and do not show errors (I use Visual Studio Code). With TypeScript we almost do not have these problems. IDE support is superb, working with types is much easier and typing system seems more mature and powerful. There are some downsides (like partion inheritance etc.), but TS team is still pushing it forward. So for me TypeScript is clear winner.

If you will start a project from scratch I recommend to use TypeScript. But, If you work with legacy projects written in JavaScript I recommend Flow (JS). Both tools have the same objective: reduce the bad code (which create illegible code, generate bugs e problems to maintenance). Flex helps you to avoid fall in bad codes, but TypeScript prevent you to c you to create bad codes. I believe cause this some JavaScript fans don't like TS, because TS block you to write some types o code. This is the fundamental difference between TS and Flow: Flow avoid problems, but no force. TS force you to prevent problems.

I use TypeScript because it's adoption by many developers, it's supported by many companies, and it's growth. AngularJS, React, @ASP.NET Core. I started using it in .NET Core, then for a job. Later I added more Angular experience and wrote more React software. It makes your code easier to understand and read... which means it makes other people's code easier to understand and read.

I use TypeScript because:

• incredible developer tooling and community support
• actively developed and supported by Microsoft (yes, I like Microsoft) ;)
• easier to make sense of a TS codebase because the annotations provide so much more context than plain JS
• refactors become easier (VSCode has superb support for TS)

I've switched back and forth between TS and Flow and decided a year ago to abandon Flow completely in favor of TS. I don't want to bash Flow, however, my main grievances are very poor tooling (editor integration leaves much to be desired), a slower release cycle, and subpar docs and community support.

Long ago when Angular 2 evolved I had to decide between the new #Angular and TypeScript or React. I really love typing my code, but forced to use TypeScript was a bit too much. I prefer the new #ECMA standard and the evolution of the old and reliable JavaScript. So finding Flow (JS) was an incredible milestone in my career as a developer. Finally, I could use types in my code, and JavaScript with the new standard. I already had the experience of CoffeeScript, so TypeScript was not an option.

From a StackShare community member: "We are looking to rewrite our outdated front-end with TypeScript. Right now we have a mix of CoffeeScript and vanilla JavaScript. I have read that adopting TypeScript can help enforce better code quality, and best practices. I also heard good things about Flow (JS). Which one would you recommend and why?"

I think our #Frontend stack is pretty standard – but we have taken some deviations from a typical modern stack:

• Flow (JS) instead of TypeScript. Flow was an easy choice 2+ years ago, as both flow and React were (and still are) maintained by Facebook. Today, it seems that the JavaScript community has settled on TypeScript as the winner. For new projects, I'd choose TS, but I don't see the point in migrating an existing project from flowtype to TS, when the end result will be roughly the same. Sure, memory usage is a bit high, and every now and then I have to kill some zombie processes, but our text editors (Sublime Text), CI scripts, and Babel are already set up to take advantage of the type safety that flow offers. When/if the React team writes React itself in TS, then I'll take a closer look – until then, flow works for us.

• Yarn instead of npm. When yarn debuted, we never looked back. Now npm has pretty much caught up with speed and lockfiles, but yarn gives me confidence that my dependency installs are deterministic. Really interested in the plug-n-play (PnP) feature that removes the need for a node_modules folder, but haven't implemented this yet.