Simple Int Array Flattener/De-nester in ECMAScript 5

flatten.js

// Simple Int Array Flattener/De-nester in ECMAScript 5!
// Interactive version on Plunker: https://plnkr.co/edit/fjqPJmzxpTFQu8VsToXK

(function(){ // Immediately Invoked Function Expression (iife) for safety closure.
  
  var firstArray =  [[1,2,[3]],4];        // Test array #1, 3 nests deep.
  var secondArray =  [[1,2,[3,[5]]],4];   // Test array #2, 4 nests deep!
  
  var flatten = function(arr){            // Our flatten function take an array.
    var flatArr = [];                     // New empty array.
    var newArr = arr.join().split(",");   // Flatten or De-nest our nested array into equal string values.
    for(var i=0; i<newArr.length; i++){   // Loop through new flattened string array.
      flatArr.push(parseInt(newArr[i]));  // Push new int values into new array.
    }
    console.log(flatArr);                 // Logging out to console so we may see the result.
  }
  
  flatten(firstArray);                    // Call the function for our first test array.
  flatten(secondArray);                   // And then call it again for the second array.
  
})();                                     // Close the closure and then immediately call itself.