flattenArray.js

//ArrayFlatter, flatens array of any nested levels
var arrayFlatter = function(){
  /**
   * Method to flatten input array.
   * @param {string} input - Input array, containing deeply nested array
  */
  this.flatArray = function(input){
    return new Array(JSON.stringify(input).replace(/[\[\]]/g,""));
  }
  
}
var input = [[1,2,[3]],4];
var arrayFlat = new arrayFlatter();
var output = arrayFlat.flatArray(input);
console.log(output);