internal/extremumBy.js

define(['./baseEach'], function(baseEach) {

  /** Used as references for `-Infinity` and `Infinity`. */
  var NEGATIVE_INFINITY = Number.NEGATIVE_INFINITY,
      POSITIVE_INFINITY = Number.POSITIVE_INFINITY;

  /**
   * Gets the extremum value of `collection` invoking `iteratee` for each value
   * in `collection` to generate the criterion by which the value is ranked.
   * The `iteratee` is invoked with three arguments; (value, index, collection).
   *
   * @private
   * @param {Array|Object|string} collection The collection to iterate over.
   * @param {Function} iteratee The function invoked per iteration.
   * @param {boolean} [isMin] Specify returning the minimum, instead of the
   *  maximum, extremum value.
   * @returns {*} Returns the extremum value.
   */
  function extremumBy(collection, iteratee, isMin) {
    var exValue = isMin ? POSITIVE_INFINITY : NEGATIVE_INFINITY,
        computed = exValue,
        result = computed;

    baseEach(collection, function(value, index, collection) {
      var current = iteratee(value, index, collection);
      if ((isMin ? current < computed : current > computed) || (current === exValue && current === result)) {
        computed = current;
        result = value;
      }
    });
    return result;
  }

  return extremumBy;
});