ES6 Pure & self documented Functions.

index.js

/**
 * ES6 Pure & self documented Functions.
 *
 * Why Pure?
 *
 * A pure function is a function where the return value is only determined 
 * by its input values, without observable side effects.
 *
 * Why Self-documented?
 *
 * Extract all the object path in the first line with the destructuring, so
 * you know all the input that the function receive.
 *
 * If you have less than 4 variables, you can declare it like:
 * function readFile (filepath, filename, permissions) {}
 *
 * Otwerwhise use object approach.
 *
 * for Async functions, pass callback after opts
 * function readFile (opts, cb) {}
 *
 */
function readFile (opts) {
  const { filepath, filename, permissions } = opts
  console.log(`reading file '${filename}' at ${filepath} with ${permissions} mode`)
}

readFile({filepath: '~/HOME', filename: 'test.txt', permissions: '644'})