It couldn't be replaced by looking at Lodash's source code, because A LOT of the alternatives here are built into Javascript, and the Lodash code is significantly larger.

Check flatten in this website:

    array.flat();

Versus Lodash:

    function baseFlatten(array, depth, predicate, isStrict, result) {
      predicate || (predicate = isFlattenable)
      result || (result = [])

      if (array == null) {
        return result
      }

      for (const value of array) {
        if (depth > 0 && predicate(value)) {
          if (depth > 1) {
            // Recursively flatten arrays (susceptible to call stack limits).
            baseFlatten(value, depth - 1, predicate, isStrict, result)
          } else {
            result.push(...value)
          }
        } else if (!isStrict) {
          result[result.length] = value
        }
      }
      return result
    }

About your point: sure, nobody has to care about all of this. But I don't see why we should give people a hard time because they do on their free time.