Flatten Nested Arrays in Javascript

flatten.js

// See this in action: https://jsfiddle.net/mikeapr4/t4x0oe9k/

// Queue-orientated solution, will work for large-scale
// nesting (50k+), however additional overhead of space (queue)
const flatten = A => {
  const output = [], queue = [...A]
  
  while (queue.length > 0) {
  	const entry = queue.shift()
    if (Array.isArray(entry)) {
    	queue.unshift(...entry)
    }
    else {
    	output.push(entry)
    }
  }  
	return output
}

// Simpler solution more likely for general use, faster and
// less memory without queue.
const flattenRecurse = A => A.reduce((output,entry) => {
  if (Array.isArray(entry)) {
    output.push(...flattenRecurse(entry))
  }
  else {
    output.push(entry)
  }
  return output
}, [])

const tests = [
	{inp: [[1,2,[3]],4], outp: [1,2,3,4]},
	{inp: [[1,2,[]],4], outp: [1,2,4]},
	{inp: [1,2,3], outp: [1,2,3]},
	{inp: [], outp: []}
]

const pass = tests.every(t => _.isEqual(flatten(t.inp), t.outp))
$('#result').append(pass ? 'all flatten passed\n' : 'some flatten failed\n');
const passRec = tests.every(t => _.isEqual(flattenRecurse(t.inp), t.outp))
$('#result').append(passRec ? 'all flattenRecurse passed' : 'some flattenRecurse failed');