According to Google research, Bitcoin and blockchain have been one of the most sought after terms for the past year, while blockchain technology itself was one of the leading development trends for 2018. Today, more companies are looking for a way to take advantage of the blockchain mania. Moreover, 50 percent of large corporations are interested in building some kind of blockchain application. So, that's very good news for software developers. Why? Blockchain is solely based on software, how to securely store, share, and maintain data (transactions). Blockchain applications can be developed with various programming languages like Go, C #, C ++, Jave or Phyton. Within this lecture, after a brief introduction to what blockchain is we will make our mini version of blockchain using Javascript. Why Javascript? Because of the simplicity and because of the fact that this programming language is a gray statement, the truth is: 9999999999999999 === 10000000000000000.