2.

Question 1

Why is it usually better to work with Objects instead of Arrays to store a collection of records?

Answer 1

Most operations involve looking up a record, and objects can do that better than arrays.

Question 2

What is a closure?

Answer 2

Closure is a function in a function. The inner function has access to the outer’s function scope and parameters even after the outer function has returned.

Question 3

What are the differences between call, apply, and bind?

Answer 3

call and apply immediately calls a function while bind creates a new function that can be invoked in the future. Arguments with call are passed in one by one, separated with a comma while apply expects an array as its argument.

Question 4

What is an event loop?

Answer 4

An event loop is responsible for executing javascript code, collecting and processing events, and executing queued sub-tasks.

Question 5

What is currying function?

Answer 5

A currying function is the process of taking a function with multiple arguments and turning it into a sequence of functions each with a single argument.

Curried functions are a great way to improve code reusability and functional composition

Question 6

What is prototype in javascript?

Answer 6

Prototypes are the mechanism by which JavaScript objects inherit from another object.

Question 7

What is memoization?

Answer 7

Memoization is an optimization technique by storing the result of expensive function calls and returning the cached results when the same inputs occur again.

Question 8

What is a higher-order function?

Answer 8

a higher-order function is a function that accepts another function as an argument or returns a function as a return value or both of them.

Map, filter and reduce are some examples of higher-order functions that are already built-in to JavaScript.

Question 9

What is event delegation?

Answer 9

Event delegation is a pattern of adding a single event listener to a parent element instead of multiple elements.

Question 10

Name some ways to handle asynchronous operation in javascript.

Answer 10

Callback is a function that is used to notify the calling instance.

Promise is an object representing the eventual completion or failure of an asynchronous operation. A pending promise can either be fulfilled with a value or rejected with a reason.
Callbacks are attached to the returned promises that make handling of asynchronous code easier and more readable.

async/await is a new addition to ES2017 which is syntactic sugar on top of promises and make asynchronous code look synchronous code.

Question 11

What is recursion?

Answer 11

Recursion is a technique for iterating over an operation by having a function call itself repeatedly until it arrives at a result.

This is most effective for solving problems like sorting or traversing the nodes of complex or non-linear data structures.

Question 12

What is Javascript?

Answer 12

it is the scripting language of the web that was initially intended to run on the browser. Today, JavaScript is used in the server.

Question 13

What is ECMAScript?

Answer 13

is a standard specification for scripting languages. JavaScript is based on ECMAScript.

Question 14

What is the difference between == and ===?

Answer 14

== compares values
=== compares both type and value

Question 15

What is a promise?

Answer 15

is an object that may produce a single value sometime in the future with either a resolved value or a reason for not being resolved

Question 16

What is strict mode in JS?

Answer 16

it is useful for writing secure JS code. It prevents some bugs from happening and throws more exceptions.

Question 17

What is the difference between null and undefined?

Answer 17

null type is an object that is explicitly assigned to a variable.

undefined type is undefined where the variable has been declared but has no assigned value

Question 18

What is AJAX?

Answer 18

stands for Asynchronous JavaScript and XML. We can send data to the server and get data without refreshing the page.

Question 19

Explain the difference between synchronous and asynchronous.

Answer 19

Synchronous is blocking operation while asynchronous is not. Synchronous complete the current code before the next code is executed while asynchronous continue on the next code without completing the current code

Question 20

What are the differences between var, let, and const

Answer 20

var is scoped to a function. let and const are block-scoped. Accessible to nearest curly braces (function, if-else, for-loop)

Question 21

What is the DOM?

Answer 21

it stands for Document Object Model. This can be used to access and change the document structure, style, and content.

Question 22

What is the difference between a property and a method on a class? / Pluralsight

Answer 22

A property is an association between a name and a value; a method is when a function is the value of a property.

Question 23

What is a major reason for adding flow control logic using the return value from an iterator’s next()? / Pluralsight

Answer 23

To decide whether or not to return {done: true} instead of {done: false}

Question 24

Given a complex object, foo, with keys that are not known ahead of time, how can you check if a given key, “k”, is in the object without iterating through the whole object? / Pluralsight

Answer 24

“k” in foo

Question 25

How can you recreate the following string with a line break into a template literal? console.log(‘string text line 1\n’ + ‘string text line 2’); / Pluralsight

Answer 25

console.log(`string text line 1

string text line 2`);

Question 26

What is the output of iterating over the following Set? / Pluralsight

let set = new Set("food");
for (let item of set) console.log(item);

Answer 26

f
o
d

Question 27

A web app has a performance-impacting function, impactFoo(), that is called around the same time that a series of async, await AJAX function calls reach completion. How can the function be deferred to be called after any pending event handlers to avoid blocking the application? / Pluralsight

Answer 27

setTimeout(impactFoo, 0);