function isIndex(value, length) {
    const 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)
}
Used to detect unsigned integer values.