Video Guide:
With WhatsApp Pocket, you can directly backup the chats, photos, videos, voice messages, etc. from your iPhone WhatsApp to computer as you like. Works with new iPhone 6 Plus, iPhone 6 and iPhone 5S, 5C, etc, from iOS 6 to iOS 8.

Moreover, if you have backed up iPhone with iTunes, you can extract the WhatsApp chats, photos audio and more from iTunes backup file with the smart program.