'@babel/register' not caching plugins and presets correctly

[pbadenski]

Dear community! :D

I was looking at long test times in our project. I recorded a CPU profile of a test run and noticed something rather odd. loadPlugin and loadPreset take over 40% of the test run and 10 seconds in total! See below:

I then ran in a debugger to see what's going on in babel core and noticed that plugins and presets somehow get reloaded all the time whereas they should be loaded from cache.

To clarify - I double checked that there is multiple calls to loadPlugin and loadPreset and they're all roughly the same time. (rather than a single slow call and many very fast ones)

Below babel-register.js we use for mocha:

const options = {
  extensions: [ ".ts", ".tsx", ".js" ],
  presets: [
    "@babel/preset-react",
    "@babel/preset-typescript",
  ],
  plugins: [
    "@babel/plugin-transform-modules-commonjs",
    "@babel/plugin-proposal-class-properties",
    "@babel/plugin-proposal-export-namespace-from",
  ],
  ignore: [ /node_modules\/(?!d3)/ ],
  babelrc: false,
  cache: true
};
require("@babel/register")(options);

Appreciate your help!

[nicolo-ribaudo]

The problem is that we still need to resolve the plugins every time. If you use require("plugin name") instead of just "plugin name" in your config, you might get a good perf boost because you completely skip Babel's resolution.

[pbadenski]

Wow, thanks, this is a great tip! This reduced our test startup time by 50-70% on average! Wish I'd knew about it earlier :D