Top Interview Questions for Backend Developers(Node)

Introduction

Being a Full Stack Developer, I had appeared for Backend Developer position as well. In this post, I will be sharing most common Backend Dev question asked to me in all those interviews except the DSA part.

Q1. Create a sleep function using Async/Await.

In the below example, the sleep function returns a promise which is resolved after given millisecond using setTimeout API.

Q2. How Javascript Engine works?

When a js file is ran,

A global execution context is created.
A memory heap is created where all variables (with var keyword) and functions (except arrow func) are declared.

In the below image we can see, variable a is declared w/o even execution has started.
A Call Stack is created which stores the line which is going to be executed.
When call stack gets a function call, it creates a functional context and the process is repeated in the functional context.
When call stack encounters WEB APIs like setTimeout/Interval/Immediate, these are sent to callback queue to process after call stack is empty.
When call stack encounters a Promise it is sent to micro task queue (higher priority than callback queue) to process after call stack is empty.
Once call stack is empty, event loop moves functions from queues to call stack for execution.