Markues

// If the flatten function is not already defined
if(typeof Array.prototype.flatten !== "function") {
  Array.prototype.flatten = function() {
    let newArray = [];
    this.forEach((current, index, array) => {
      // If the current item is an array
      if(current.constructor === Array) {
        // Recursively call flatten on that item and concatenate
        // it to our final array
        newArray = newArray.concat(current.flatten());