My requirement is like - When an item is added to a list, a log should be added to another list? And this needs be done using JSOM. is there a way to achieve this using JSOM?
Assuming that your scenario is O365, the standard approach would be to use Remote Receivers. Those xan be attached to the list and perform operations when events occur, such as adding, removing, modifying, etc.
The following post is a good starting point: https://msdn.microsoft.com/en-us/library/office/jj220043.aspx
You have two options here: 1.) Use Jquery to add an additional click event on Submit button and write JS code to make entry to the log list. To achieve this simply add a content editor on you new item form. Something similar to https://stackoverflow.com/questions/6527783/call-submit-button-function-from-jquery
2.) Use the Pre save event of Sharepoint https://deannaschneider.wordpress.com/2012/12/03/sp2010-using-presaveaction-on-custom-forms/