Flaten Array using javascript

flattenArray.js

var originalArray = [1, [2], [3, 4, [5, [6,7]]]];

 function flatten(arr) {
      var flattenarr = [];
     arr.forEach(item => {
         if(Array.isArray(item)) {
             var arrItem = item;
             while(Array.isArray(arrItem)) {
                 arrItem.forEach(next => {
                     if(Array.isArray(next)) {
                         arrItem = next;
                     } else {
                         flattenarr.push(next);
                         arrItem = next;
                     }
                 });
             }
         } else {
           flattenarr.push(item);
         }
    });
     return flattenarr;
 }
  var newArray = flatten(originalArray);
console.log(newArray);