gistfile1.txt

// Recursively concat nested array
function concatR(ar, result) {
   result = result || []
   for(var i=0; i < ar.length; i++) {
       if (Array.isArray(ar[i])) {
          // calling with inner array
          concatR(ar[i], result)
       } else {
          result.push(ar[i])
       }
   }
   return result
}

// For simple test assert
function assert(ar, json) {
   var ok = JSON.stringify(concatR(ar)) == json
   if (ok) {
       console.info("Passed: ", json)
   } else {
       console.error("Failed: ", json)
   }
}


assert([[1,2,[3]],4], "[1,2,3,4]")
assert([[1,2,[3,[]]],4], "[1,2,3,4]")
assert([1,2,3,4], "[1,2,3,4]")