Code Sample: Array Flattener

flattener.js

const assert = require('assert')

assert.deepEqual(flatten([[1,2,[3]],4]), [1,2,3,4])

/**
 * Returns a flattened array.
 * @param {array} input 
 * @param {array=} output
 */
function flatten (input, output = []) {
  input.forEach((element) => {
    if (Array.isArray(element)) {
      output.concat(flatten(element, output))
    } else {
      output.push(element)
    }
  })

  return output
}

node flattener.js shouldn’t output anything unless the assertion on line 3 fails.