// 'flatten' flattend arbitrary nested value sequences into
// a single array of values
const flatten = (input: []): number[] => {

  const flattened: number[] = []

  for (let i = 0; i < input.length; i++) {
    // If current value is an array, call flatten on it too
    if (Array.isArray(input[i])) {
      // flatten returned array with spread operator
      flattened.push(...flatten(input[i]))
    } else {
      // If value is a primitive, push it into answer array
      flattened.push(input[i])
    }
  }

  return flattened
}

module.exports = flatten

//// Tests
//// Since you guys asked for a single file, I've added the commented tests below :)
/*
const flatten = require('./flatten.ts')

describe('flatten', () => {

  expect(flatten([
    [1, 2, [3]], a
    4
  ])).toEqual([
    1, 2, 3, 4
  ])

  expect(flatten([
    [1, [2, [3]]],
    [[4]]
  ])).toEqual([
    1, 2, 3, 4
  ])

  expect(flatten([
    [[[[[[[[1]]]]]]], 2],
    [[3], [[[[[[4]]]]]]], 5
  ])).toEqual([
    1, 2, 3, 4, 5
  ])

})
*/