Flatten array

flatten.js

//flatten:: a -> a -> a
var flatten = function(arr, result){
  
  result = result || [];
  
  arr.map(function(entry){
    
    if(Array.isArray(entry)){
      //call flatten recursively since entry is an array
      return flatten(entry,result);
      
    } else{
      //push to result if entry is not an array
      result.push(entry);
      
    }
    
  });
  
  return result;
}

Test the above gist by console.log(flatten([[1,[2],[3]],4,[5,6,[7,[8,9,[10,11]]]]]));