Data Types in JavaScript

Question 1

This 64 bit format is used to store numbers in JS

Answer 1

IEEE-754

Question 2

use this method to convert a number to string

Answer 2

.toString(base)

Question 3

this is the value numbers pick if they overflow storage

Answer 3

Infinity

Question 4

4 most used rounding functions

Answer 4

Math.round
Math.ceil
Math.floor
Math.trunc

Question 5

does NaN equal itself?

Answer 5

No

Question 6

character encoding of strings in JS

Answer 6

UTF-16

Question 7

Strings are immutable in JS. True/False

Answer 7

True

Question 8

In JS lowercase alphabets are greater than Uppercase alphabets

Answer 8

True

Question 9

Names of codePoint methods

Answer 9

codePointAt() —> gives unicode value

fromCodePoint() —> gets unicode character from integer value

Question 10

localeCompare is used to compare two ____?

Answer 10

strings

Question 11

What does the at() function do in an array

Answer 11

it fetches the element at position i;

if i is negative, it counts backwards.

Question 12

Arrays extend objects in JavaScript. True / False ?

Answer 12

True

Question 13

It is possible to add non-numeric key in an array. True / False ?

Answer 13

True, this is an inconvenience as programmer needs to be alert.

Question 14

The length property in array is the number of elements in the array. True or False ??

Answer 14

False, it is the largest numeric index + 1.

Question 15

This is the fastest and easiest way to clear an array in JS.

Answer 15

arr.length = 0;

length once reduced, truncates the array, and cannot be reassigned to its initial value.

Question 16

The splice method returns this ____

Answer 16

the list of removed elements.

Question 17

Symbol.iterator is used for ____

Answer 17

making an object iterable in the for…of loop

Question 18

the 7 main methods of map are

Answer 18

new Map() - create map;

map. set(key, value) - insert key, value pair in map
map. get(key) - get the value of key
map. has(key) - true if key exists; false otherwise
map. delete(key) - remove value by key
map. clear() - remove all elements of map
map. size() - returns count of elements in map

Question 19

What is SameValueZero

Answer 19

It is the algorithm maps use to compare keys; it is like strict equality, but only NaN is equal to NaN.

Question 20

Map preserves the order of insertion. True / False ?

Answer 20

True. Objects are the ones that do not store values in inserted order.

Question 21

The six methods of set are

Answer 21

new Set(iterable);

set. add(value);
set. delete(value);
set. has(value);
set. clear();
set. size();

Question 22

Reflect.ownKeys(obj) returns ___

Answer 22

all keys; even symbolic ones.

Question 23

Object.getOwnPropertySymbols(obj) returns ___

Answer 23

only symbolic keys

Question 24

strings are iterables is JavaScript. True / False ?

Answer 24

True

Question 25

for(let [key, value] of Object.entries(obj)) {...} | Which JS feature allows key, and value to be broken up as such?

Answer 25

destructuring

Question 26

use destructuring to get all default values in an object

Answer 26

functionCall( { } );

Question 27

JSON.stringify works on primitives. True / False ?

Answer 27

True

Question 28

JSON.stringify works on arrays. True / False ?

Answer 28

True

Question 29

Strings in JSON object use single ticks, and backticks. True or False ?

Answer 29

False

Question 30

what is the first key, value pair the replacer function puts in JSON format

Answer 30

:[object Object]

Question 31

JSON.stringify gives an error in this case of object reference

Answer 31

circular reference

Question 32

In JS we can call any function with any number of arguments no matter how it is defined. True or False ?

Answer 32

True; but extra arguments will be ignored.

Question 33

arrow functions do not have "this" and they do not have their own ____ object either

Answer 33

argument; which stores the argument list.

Question 34

What is hoisting?

Answer 34

The phenomenon in which variables declared with "var" are automatically moved to top of function declaration irrespective of their declaration in the function.

Question 35

browser:window :: Node.js:____

Answer 35

global; | it is the name of the global object

Question 36

name of a generalized global object that was recently added to the language ____

Answer 36

globalThis

Question 37

alert/confirm/prompt makes timer stop. True or False ?

Answer 37

False.

Question 38

multiple event handlers are executed in this order ___

Answer 38

in the order that they are written.