firebase-tools/lib/detectProjectRoot.js

'use strict';

var fs = require('fs');
var path = require('path');

module.exports = function(cwd) {
  var projectRootDir = cwd || process.cwd();
  while (!fs.existsSync(path.resolve(projectRootDir, './firebase.json'))) {
    var parentDir = path.dirname(projectRootDir);
    if (parentDir === projectRootDir) {
      return null;
    }
    projectRootDir = parentDir;
  }
  return projectRootDir;
};