|  | /** Used as references for various `Number` constants. */ | 
|  | var MAX_SAFE_INTEGER = 9007199254740991; | 
|  |  | 
|  | /** Used to detect unsigned integer values. */ | 
|  | var reIsUint = /^(?:0|[1-9]\d*)$/; | 
|  |  | 
|  | /** | 
|  | * 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) { | 
|  | var type = typeof value; | 
|  | length = length == null ? MAX_SAFE_INTEGER : length; | 
|  |  | 
|  | return !!length && | 
|  | (type == 'number' || | 
|  | (type != 'symbol' && reIsUint.test(value))) && | 
|  | (value > -1 && value % 1 == 0 && value < length); | 
|  | } | 
|  |  | 
|  | module.exports = isIndex; |