J Bruni's "getFlattenedIntegers"

getFlattenedIntegers.js

/*** Running CodePen available at http://codepen.io/anon/pen/VKyAVw ***/

/**
 * Flatten an array of arbitrarily
 * nested arrays of integers into
 * a flat array of integers.
 */
function getFlattenedIntegers(integers) {
  var result = []

  function pushInt(value) {
    if (typeof value === "number") {
      if (value === parseInt(value)) {
        // Push into results if value is an integer
        result.push(value)
      }
    }
    else if (isArray(value)) {
      // Loop through all values if value is an array
      value.forEach(function(item) {
        pushInt(item)
      })
    }
  }

  pushInt(integers)

  return result
}

/**
 * Check if value looks like an array
 */
function isArray(value) {
  if (typeof value === 'undefined') return false
  if (value === null) return false 
  return ((typeof value.length === 'number')
          && (typeof value.forEach === 'function'))
}


/*** Tests ***/

/**
 * Expected inputs + outputs to test against.
 */
var tests = [
  {
    input:  [[1,2,[3]],4],
    output: [1,2,3,4]
  }, {
    input: [[9,[8,7,6],5],4,[3,2],[1]],
    output: [9,8,7,6,5,4,3,2,1]
  }, {
    input: [5],
    output: [5]
  }, {
    input: 5,
    output: [5]   // auto-converts to array (assumption)
  }, {
    input: '5',
    output: []   // not an integer
  }, {
    input: [[[[1], 2], 3],null,5,'hi',[7,[7.5],8],NaN,Infinity],
    output: [1,2,3,5,7,8]   // ignores non-integer values
  }
]

/**
 * Compares result with expected output
 */
function checkResult(result, expected) {
  var max = result.length;
  if (max !== expected.length) {
    return false
  }
  for (var i = 0; i < max; i++) {
    if (result[i] !== expected[i]) {
      return false
    }
  }
  return true
}

/**
 * Run "test suite" outputting the results
 */
document.write('<pre>')
tests.forEach(function(test){
  var result = getFlattenedIntegers(test.input)
  var passed = checkResult(result, test.output)
  document.write('input: ' + test.input + '\n')
  document.write('output: ' + result + '\n')
  document.write('expected: ' + test.output + '\n')
  document.write('result: <b>' + (passed ? 'passed' : 'failed') + '</b>\n\n')
})
document.write('</pre>')