Web Developer

The event loop allows Node.js to perform non-blocking I/O operations despite the fact that JavaScript is single-threaded. It is done by assigning operations to the operating system whenever and wherever possible. Most operating systems are multi-threaded and hence can handle multiple operations executing in the background. When one of these operations is completed, the kernel tells Node.js and the respective callback assigned to that operation is added to the event queue which will eventually be executed. 

Features of Event Loop :
Event loop is an endless loop, which waits for tasks, executes them and then sleeps until it receives more tasks.
The event loop executes tasks from the event queue only when the call stack is empty i.e. there is no ongoing task.
The event loop allows us to use callbacks and promises.
The event loop executes the tasks starting from the oldest first.

Node.js is an open-source and cross-platform runtime that build on top chrome’s v8 JavaScript engine. Basically, now a days it is very popular. Many server uses node.js to run applications.
Node basically runs a single thread, but what it does when the request comes it sends that request to some other workers, that workers process the request. The request may I/O operation or fetching data from the database or interacting with some other servers to perform the operation

Third party APIs are APIs provided by third parties — generally companies such as Facebook, Twitter, or Google — to allow you to access their functionality via JavaScript and use it on your site. One of the most obvious examples is using mapping APIs to display custom maps on your pages.

The main advantage of using promise is you get an object to decide the action that needs to be taken after the async task completes. This gives more manageable code and avoids callback hell.

Tip 1 : The cross questioning can go intense some time, think before you speak.

Tip 2 : Be open minded and answer whatever you are thinking, in these rounds I feel it is important to have opinion.

Tip 3 : Context of questions can be switched, pay attention to the details. It is okay to ask questions in these round, like what are the projects currently the company is investing, which team you are mentoring. How all is the work environment etc.