logger.js

const DEBUG = JSON.parse(process.env.DEBUG) || false;

const logger = wrapped => (...args) => {
  const results = wrapped(...args);
  if (DEBUG) {
    console.log(`Function: ${wrapped.name}; ${args} => ${results}`);
  }
  return results;
};

const adder = logger(function adder(a, b) {
  return a + b;
});

console.log(adder(1, 2));

// node logger.js
// 3

// DEBUG=true node logger.js
// Function: adder; 1,2 => 3
// 3