lodash/internal/baseFlatten.js

define(['./arrayPush', '../lang/isArguments', '../lang/isArray', './isArrayLike', './isObjectLike'], function(arrayPush, isArguments, isArray, isArrayLike, isObjectLike) {

  /**
   * The base implementation of `_.flatten` with added support for restricting
   * flattening and specifying the start index.
   *
   * @private
   * @param {Array} array The array to flatten.
   * @param {boolean} [isDeep] Specify a deep flatten.
   * @param {boolean} [isStrict] Restrict flattening to arrays-like objects.
   * @param {Array} [result=[]] The initial result value.
   * @returns {Array} Returns the new flattened array.
   */
  function baseFlatten(array, isDeep, isStrict, result) {
    result || (result = []);

    var index = -1,
        length = array.length;

    while (++index < length) {
      var value = array[index];
      if (isObjectLike(value) && isArrayLike(value) &&
          (isStrict || isArray(value) || isArguments(value))) {
        if (isDeep) {
          // Recursively flatten arrays (susceptible to call stack limits).
          baseFlatten(value, isDeep, isStrict, result);
        } else {
          arrayPush(result, value);
        }
      } else if (!isStrict) {
        result[result.length] = value;
      }
    }
    return result;
  }

  return baseFlatten;
});