What is Unobtrusive JavaScript ?

Unobtrusive is best practice of writing the JavaScript or JQuery in the decouple or separation format means -

When we write the JavaScript or JQuery - we usually followed the practice of writing the Presentation and behavior in one line only - which is not best practice e.g.

Unobtrusive means decouple or separation of presentation and behavior of object which help in cleaning and maintaining  the code and move out the entire behavior section in separate JS file. e.g.