merge-tsconfig.js

#!/usr/bin/env node

const isScalar = (v) => {
  return !(v === null || v === undefined || typeof v === 'object');
};

const mergeObject = (a, b) => {
  const keys = new Set([...Object.keys(a), ...Object.keys(b)]);
  const accum = {};
  for (const k of keys) {
    const va = a[k];
    const vb = b[k];
    if (va !== undefined && vb !== undefined) {
      if (isScalar(va)) {
        accum[k] = vb;
      } else {
        accum[k] = merge(va, vb);
      }
    } else {
      accum[k] = [va, vb].find(e => e !== undefined);
    }
  }
  return accum;
};

const mergeArray = (a, b) => {
  return [...a, ...b];
};

const merge = (a, b) => {
  if (Array.isArray(a)) {
    return mergeArray(a, b);
  } else {
    return mergeObject(a, b);
  }
};

const tsconfigPaths = process.argv.slice(2);
const tsconfigs = tsconfigPaths.map(path => require(`./${path}`));
const merged = tsconfigs.reduce((accum, config) => {
  return merge(accum, config);
}, {});
console.log(JSON.stringify(merged));