The Internet of Things (IoT) paradigm enables the development of new kinds of mass market applications that benefit from environment data collected by sensors. Because of the huge number of objects encompassed by the IoT, their impermanence and their world wide accessibility, the middleware community faces new challenges. Offering application developers the possibility to declare IoT variables easily discovered and transparently updated is one of these challenges. IoT systems are supported by distributed architectures where sensors and end-user applications interact through IoT platforms deployed on the cloud or on the edges. In this paper, we describe the IoTVar middleware that manages interactions between end-user applications and IoT platforms through IoTVar proxies. We show how IoTVar enables software developers to declare and manage IoT variables with a minimum number of lines of code.