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Using node-config with TypeScript

When we migrated one of our projects from ES6 to TypeScript, we discovered something really crazy: the heap memory it allocated increased by factor 20. We found out that node-config was the reason.

I should mention that we have a backend Node application, written in TypeScript, compiled to ./build, started with node build/src/index.js, dockerized and deployed to k8s -- and, it is using node-config.

node-config is a handy library used by many projects. It provides hierarchical, environment-sensitive (NODE_ENV) configuration for your application. All configuration files are maintained in a config directory ./config. Very nice.

If you are using TypeScript, you usually compile to something like ./build or ./dist and run your application from there. The funny thing about node-config is that it still reads the configuration files from ./config (by default), even if there is something like ./build/config.

Furthermore, if the config directory contains .ts files, node-config will compile them on-the-fly. That's great during development. But not so great in production.

Try it yourself. I have set up a minimal project as a showcase.

// prepare
$ npm ci
$ npm build

$ npm run start:bad
> node build/src/index.js

foo = bar
heapUsed = 68,912,656 [byte]
startup time = 985 [ms]

$ npm run start:good
> NODE_CONFIG_DIR=./build/config node build/src/index.js

foo = bar
heapUsed = 3,298,992 [byte]
startup time = 14 [ms]

How did we solve the problem?

  • Simply compile ./config to ./build/config along with the rest of the TypeScript code which goes to ./build/src.
  • Make sure that node-config reads the configs from the compiled version ./build/config by setting the NODE_CONFIG_DIR environment variable.
  • Post-process all compiled .js files in ./build/config to make them work with node-config because it doesn't parse exports.default as generated by tsc. Replace it with module.exports. Feels hacky, yes. But I have seen other projects doing a bit of post-processing after tsc.

I'm sure there are other solutions. Please let me know.

Maybe it helps.