lodash/internal/isIndex.js

define([], function() {

  /**
   * Used as the [maximum length](https://people.mozilla.org/~jorendorff/es6-draft.html#sec-number.max_safe_integer)
   * of an array-like value.
   */
  var MAX_SAFE_INTEGER = 9007199254740991;

  /**
   * Checks if `value` is a valid array-like index.
   *
   * @private
   * @param {*} value The value to check.
   * @param {number} [length=MAX_SAFE_INTEGER] The upper bounds of a valid index.
   * @returns {boolean} Returns `true` if `value` is a valid index, else `false`.
   */
  function isIndex(value, length) {
    value = typeof value == 'number' ? value : parseFloat(value);
    length = length == null ? MAX_SAFE_INTEGER : length;
    return value > -1 && value % 1 == 0 && value < length;
  }

  return isIndex;
});