Object.entries = Object.entries || function (obj) {
  var ownProps = Object.keys(obj),
    i = ownProps.length,
    resArray = new Array(i); // preallocate the Array
  while (i--)
    resArray[i] = [ownProps[i], obj[ownProps[i]]];

  return resArray;
};
Object.fromEntries = Object.fromEntries || function (arr) {
  let obj = {};
  arr.forEach(([k, v]) => obj[k] = v)
  return obj;
}
if (!Array.prototype.flat) {
  Object.defineProperty(Array.prototype, 'flat', {
    value: function (depth) {
      let res = [],
        depthArg = depth || 1,
        depthNum = 0,
        flatMap = (arr) => {
          arr.map((element, index, array) => {
            if (Object.prototype.toString.call(element).slice(8, -1) === 'Array') {
              if (depthNum < depthArg) {
                depthNum++;
                flatMap(element);
              } else {
                res.push(element);
              }
            } else {
              res.push(element);
              if (index === array.length - 1) depthNum = 0;
            }
          });
        };
      flatMap(this);
      return res;
    }
  });
}