Question: On click of button, I need to make an ajax request to the back-end to persist the current time and some more details in the database. So, if the user clicks the button multiple times continuously, multiple ajax requests will be fired to the back-end. I want these requests to be executed in a sequential way one after the other and I don't need to keep track of the success/failure of ajax request in the front-end. How to handle these scenarios?

Answer: 
you can use promises to trigger a particular function on the fulfillment of an async request. <https://docs.angularjs.org/api/ng/service/>$q
When you call ajax call
just add 

> 
> async: false
>  or async: true
> 
> 
> 

in function, the call will synchronise or not