How to get selected records ID from List View using Javascript / Ajax Toolkit, when custom button is added on List View page

How to get selected records ID from List View using Javascript / Ajax Toolkit, when custom button is added on List View page

Create a new Button on Lead of type List Button. Add the button on Lead List View Layout and write below Javascript code:

{!RequireScript("/js/functions.js")}

var recordsSelected = {!GetRecordIds($ObjectType.Lead)}

for(var i=0; i < recordsSelected .length ; i++) {

     alert('Selected ID '+recordsSelected[i]);

}