Usually when you are building microcontroller project (say Arduino), you need to write code first, upload to microcontroller and then run it. And if you need to change something or run different program, you need to flash new program in to it. But these things can be done differently – by using script language like Java Script. Basically this works like this – an interpreter program continuously runs on microcontroller which accepts and runs scripts written by user during run time. This gives less hustle on developing things. You don’t need development tools like compiler or download cables. Scripting language is hig level language, where lots of things are hidden and you need to write less code. Also your programs are executed immediately once typed.