Maybe:

const err = new Error(`The function passed to the fourth parameter of safelyRead crashed')
  Called with ${JSON.stringify(arguments)}
`;

console.error(err);

When trying to run the main file index.js in the browser without a bundler (webpack, etc), the 'require' function and 'process.env.NODE_ENV' are undefined. Maybe add a bundler?

I'm using microbundle in my packages with the following relevant fields on package.json:

{
  "source": "src/index.ts",
  "main": "dist/index.umd.js",
  "module": "dist/index.js",
  "scripts": {
    "build": "microbundle -f esm,umd --target node,web --strict --name safelyRead",
  },
}

This will output a umd and a module file. The UMD file works everywhere and webpack loves the module file because it allowes treeshaking.

Maybe remove lodash.get dependency and implement the get function ourselves is a good ideal to prevent us from having to update this library everytime lodash.get changes.

A get implementation using ES5, which runs everywhere:

function get (object, path, value) {
  const pathArray = Array.isArray(path) ? path : path.split('.').filter(key => key);

  const pathArrayFlat = Array.prototype.concat.apply(
    [],
    pathArray.map(part => typeof part === 'string' ? part.split('.') : part)
  );

  return pathArrayFlat.reduce((obj, key) => obj && obj[key], object) || value;
}

What do you think?

--

By the way, I got the function above from here and rewrote it to stop using flatMap since it doesn't run everywhere.