Node.js Interview Questions and Answers

Buffer

It is a global class that can be accessed in an application without importing the buffer module. It can be constructed in a variety of ways like var buf = new Buffer(5);

Use of a buffer in Node JS

Buffer is used to dealing with TCP streams, reading, and writing data to the filesystem in the Node.js server, which are purely binary teams of data.

It is designed in a way that is easy to manage, faster and has an API designed for binary data, which makes it the perfect choice for handling streams of data.

Stream

these are the objects that allow the developers to read the data from the source or can write the data to the destination in an endless manner. They usually have problems with the large data. With a stream, there is no need to wait for the whole resource to load.

There are different types of Stream:

• Readable
• Writable
• Duplex
• Transfer

A pipe is a function that reads the data from a readable stream once it is available and writes it in the destination writable stream. It performs all the reasonable things including the errors, files in case any one side falls apart. In due case, piping redirections any readable stream to a writable stream.

open() function is used to opens a file by passing a file name.

Syntax : fs.open(path, flags[mode], callback)

Parameters

• path : It is a string having file name with complete path
• flags : It indicates the behavior of the file to be opened
• mode : It sets the file mode like permission
• callback : gets two arguments (err, fd)

setTimeout() : It can be used to schedule code execution after a designated amount of milliseconds.

function myFunc(arg) {
  console.log(`arg was => ${arg}`);
}
setTimeout(myFunc, 1500, 'funky');

clearTimeout()  :  It can be used to cancel timeout which are set by setTimeout().

console.log('before immediate');
setImmediate((arg) => {
   console.log(`executing immediate: ${arg}`);
}, 'so immediate');
console.log('after immediate');

The timing feature of node.js contains all the necessary functions that are required to execute code after any specific period. As it is built on the V8 JavaScript engine of Google Chrome, hence its library permits the fast execution of code. Timers also provide a number of ways for managing schedules. They don't need to be imported as all the methods are easily available for the browser.

Some modules are –

• setTimeout
• setInterval
• setImmediate
• clearImmediate(immediate)
• clearTimeout(timeout)

Error-first callbacks are generally used to pass errors as well as data. It is important to pass the error as the first parameter, and then you must check if something went wrong. There are additional arguments that are used to pass data.

Reactor Pattern is used for non-blocking Input/Output operations in the Node.js. This pattern provides a handler that is associated with I/O operations. When I/O requests are generated, they get submitted to a demultiplexer, which handles concurrency in non-blocking I/O mode and collects requests in the form of an event and queues the events.

Note: This Node js interview questions have been created by Node.js Experts. It shall help you to answer some of the most frequently asked questions during a job interview.

• newListener
• removeListener
• EventEmitter: 'removeListener'
• EventEmitter. listenerCount (emitter, eventName)
• EventEmitter.defaultMaxListeners
• emitter.addListener(eventName,listener)
• emitter.emit(eventName[,...args])

A test pyramid is a metaphor that helps the grouping of software tests in a bunch of different granularity. Unit testing pyramid number of tests gets easily fitted.

For instance, unit testing, component testing, integration testing, system testing, end-to-end testing, UI testing, and others. The primary example of it is creating a unit test which will be the fastest and reliable.