Sep 13 2017

TypeScript as ES2015/ES2016+ compiler

Published by at 6:51 am under Technology   

I frequently encounter packages on NPM which bring in Babel to compile ES2015/2016+ down to older JavaScript suitable for a wider range of browsers. Babel is a very effective tool for this, it has been around quite a long time, and is highly configurable and flexible in future ready. It has an amazing community and reputation.

But – it is also surprisingly “heavy” in its impact on your tools installation. A typical Babel installation with a typical set of plug-ins can easily bring in 20,000 or more files, spread over hundreds of transitive dependency packages. On a huge project this might not be noticed, but on a small or medium project it can easily be the largest dependency.

Are large NPM dependency trees a problem? Theoretically no, but practically they have some downsides. Dependencies bring risk, and lots of dependencies inevitably bring more risk. If you depend transitively on hundreds more packages, your project is more vulnerable to the sort of NPM vagaries that happen from time to time (the most famous being left-pad), your project is more inclined to fall behind current versions, and most annoyingly in corporate settings, that long list of plugins and transitive dependencies is more likely to cause heartburn among lawyers who evaluate licenses.

There is an easy way to ease this problem, but it involves a minor update to one’s thinkinh. Find the spot in your mind where you may think:

“the TypeScript compiler is a tool for compiling TypeScript code to JavaScript and type checking it”.

The actual truth in 2017 is:

The TypeScript compiler is an excellent, well supported, frequently-updated general-purpose tool very suitable for non-TypeScript users. It does a great job compiling a broad array of standards-path ES2015/16/+ features down to ES2015 or ES5. It fits in well with overall project build tooling. It is completely suitable to use the TypeScript compiler on a non-TypeScript project for this purpose.

The TypeScript compiler has several substantial practical benefits over Babel:

  • It is a single dependency with no transitive dependencies.
  • Usually faster compilation.
  • It is developed by a team at Microsoft, who do a great job grinding away at the boring aspects of this work, shipping a long series of updates which keep fixing bugs and adding features.
  • It installs quickly and has far fewer failure modes in installation (because of no transitive dependencies).
  • Just one open source license to review (no transitive dependencies)… from a company that your company probably already buys a lot of stuff from anyway.
  • Just one version to update, and one configuration file to tweak which features you are using.
  • WebPack and other plug-ins available, quite analogous to Babel.

As of 2017, my recommendation is to consider TypeScript as the default solution for compiling ES2015/16+ code in non-TypeScript projects, and use Babel as a fallback if your project needs cutting-edge features that are (intentionally) not yet in TypeScript.

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