code: function isEqualWith(value, other, fn) {
    if (!isFunction(fn)) {
      return isEqual(value, other);
    }
    return !!fn(value, other);
  }
docs: @param {*} value The value to compare.
  @param {*} other The other value to compare.
  @param {Function} [fn] The function to customize comparisons.
  @returns {boolean} Returns `true` if the values are equivalent, else `false`.
  @example
  
  function isGreeting(value) {
  return /^h(?:i|ello)$/.test(value);
  }
  
  function customizer(objValue, othValue) {
  if (isGreeting(objValue) && isGreeting(othValue)) {
  return true;
  }
  }
  
  var array = ['hello', 'goodbye'];
  var other = ['hi', 'goodbye'];
  
  _.isEqualWith(array, other, customizer);  // => true