lodash/_baseSum.js

/**
 * The base implementation of `sum` and `sumBy`.
 *
 * @private
 * @param {Array} array The array to iterate over.
 * @param {Function} iteratee The function invoked per iteration.
 * @returns {number} Returns the sum.
 */
function baseSum(array, iteratee) {
  let result;
  let index = -1;
  const length = array.length;

  while (++index < length) {
    const current = iteratee(array[index]);
    if (current !== undefined) {
      result = result === undefined ? current : (result + current);
    }
  }
  return result;
}

export default baseSum;