Nodejs Utililty Methods Array Flat Map

Array.prototype.flatMap = function(callback) {
  var inputArray = this;
  var start = function(value, index, length) {
    flatEach(value.shift());
    ++index != length && start(value, index, length);
    return value;
  var flatEach = function(eachValue) {
    return Array.isArray(eachValue) ? start(eachValue, 0, eachValue.length) : inputArray.push(callback(eachValue));
...

Array.prototype.flatMap = function (cb) {
  return this.map(cb).reduce(function (arr, c) { return arr.concat(c); }, []);
};

Array.prototype.flatMap = function(fn, ctx) {
  return this.reduce((k, v) => k.concat(fn.call(ctx, v)), []);
};

Array.prototype.flatMap = function(lambda) { 
      return Array.prototype.concat.apply([], this.map(lambda)); 
};

Array.prototype.flatMap = function(lambda) {
    return [].concat(this.map(lambda));
};

Array.prototype.flatMap = Array.prototype.flatMap || function(lambda) {
  return Array.prototype.concat.apply([], this.map(lambda));

Array.prototype.flatMap = function(mapFunc) {
  var result = []
  for (let item of this) {
    let tokens = mapFunc(item)
    result = result.concat(tokens)
  return result

Array.prototype.flatMap = function(projection) {
    return this.
        map(function(item) {
            return projection(item);
        }).
        mergeAll();