Check if a RadioButton (RadioGroup) is checked or not using JavaScript

Here Mudassar Ahmed Khan has explained with an example, how to check if a RadioButton or RadioGroup (i.e. set of RadioButtons) is checked (selected) or not checked (not selected) using JavaScript. When the RadioButton is clicked based on whether it is checked (selected) or unchecked (unselected), the HTML DIV will be shown or hidden using JavaScript.