Flatten an array of arrays

// Why would we do this? Well, JSON structure and NoSQL concepts come into play here:
// aka a document having a collection of authors, collection of editions, collection
// of chapters, each of those "sub arrays" having other subarrays and so on

// the following is javascript syntax - although I believe JS now has its own .flatten()
// method - I decided to code this out with recursion. It may be interesting to code this
// up in python and java as well to see how the code base compares

// for now, going to limit this to expect an array passed
function myFlatten(inArr) {
  if (! Array.isArray(inArr)) throw new Error('myFlatten() called with non-array');
  
  // put array scope out here so its availble across recursive calls
  let flatResult = [];
  
  // note: if recursion depth is a concern, could make maxDepth, checkDepth variables
  // to limit levels. Then mod the function below to increment/decrement the 
  // checkDepth - checking against maxDepth to short-ciruit another recursive call
  
  function flattenArray(inArr) {
    for (let item of inArr) {
      if (Array.isArray(item)) {
        flattenArray(item);
      } else {
        flatResult.push(item);
      }
    }
  }
  flattenArray(inArr);
  return flatResult;
}