This is a tool that allows for processing layered configuration files

Layered configuration files are quite useful when one wants to describe the configuration for different environments in terms of deltas. Most of the time one needs to override properties from a base environment in order to minimize duplication in configuration and thus minimize the risk of mistakes.

The files are merged based on an additive principle, so if you have a base file

{
  "key1": "1a",
  "key2": "2a",
  "subtree": {
    "key3": "3a",
    "key4": "4a",
    "key5": "5a"
  }
}

and an overlay file

{
  "key1": "1b",
  "subtree": {
    "key3": "3b",
  }
}

then you will get a final outcome of

{
  "key1": "1b",
  "key2": "2a",
  "subtree": {
    "key3": "3b",
    "key4": "4a",
    "key5": "5a"
  }
}

It is also possible to have multiple layers.

Often you will want to process a directory of files. Then you can use a naming convention for the top level directories:

a
b-from-a
c-from-b

How to run the program:

$ DEBUG=* node index.js sample c ./out