JavaScript-Developer-I Practice Questions

The correct answers are B and D .

A strong test case checks whether the actual output matches the expected behavior of the function.

For Option B :

let res = fizzbuzz(15);

console.assert(res === ' fizzbuzz ' );

The number 15 is divisible by both 3 and 5:

15 % 3 === 0

15 % 5 === 0

So the correct return value is:

' fizzbuzz '

That makes option B a valid test.

For Option D :

let res = fizzbuzz(Infinity);

console.assert(res === ' ' );

Infinity is not a normal finite divisible number. In JavaScript:

Infinity % 3

Infinity % 5

produce NaN, and comparisons such as:

Infinity % 3 === 0

are false.

So a typical fizzbuzz implementation would not treat Infinity as divisible by 3 or 5, meaning it should return:

' '

That makes option D a valid test for the “neither divisible by 3 nor 5” path.

Now compare the incorrect options:

Option A is wrong because:

fizzbuzz(3)

should return:

' fizz '

not:

' buzz '

Option C is wrong because the function specification says the function returns strings such as ' fizz ' , ' buzz ' , ' fizzbuzz ' , or ' ' . It does not say the function returns numeric NaN.

So this assertion is not appropriate:

console.assert(isNaN(res));

Therefore, the verified answers are B and D .

The correct answers are A, B, and D .

The two variables are:

let str1 = ' Java ' ;

let str2 = ' Script ' ;

The goal is to combine them into:

JavaScript

Option A is correct because template literals can insert variables directly into a string:

`${str1}${str2}`

This becomes:

`${ ' Java ' }${ ' Script ' }`

Result:

JavaScript

Option B is correct because strings have a concat() method:

str1.concat(str2);

This joins str2 onto the end of str1.

Result:

JavaScript

Option D is correct because the + operator performs string concatenation when both operands are strings:

str1 + str2;

This becomes:

' Java ' + ' Script '

Result:

JavaScript

The incorrect options:

Option C is not valid JavaScript for joining strings. const is used for declaring constants, not concatenating values.

Option E is incorrect because join() is an array method, not a string method. This would only work with an array, for example:

[ ' Java ' , ' Script ' ].join( ' ' );

But str1 is a string, so:

str1.join(str2)

is invalid.

Therefore, the verified answers are A, B, and D .

The correct answers are B, C, D, and E .

JavaScript browser consoles support string substitution in several console output methods. String substitution means using placeholders such as:

%s

%d

%i

%f

%o

%O

%c

Example:

console.log( " User name is %s and age is %d " , " Alex " , 25);

Output:

User name is Alex and age is 25

The valid console methods from the given options are:

Option

Method

Correct?

Reason

A

message

No

console.message() is not a standard console method.

B

log

Yes

console.log() supports formatted string substitution.

C

assert

Yes

console.assert() can output a formatted message when the assertion is false.

D

info

Yes

console.info() supports formatted output like console.log().

E

error

Yes

console.error() supports formatted output and displays an error-style message.

Example with these valid methods:

console.log( " Name: %s " , " John " );

console.info( " Score: %d " , 95);

console.error( " Error code: %d " , 500);

console.assert(false, " Failed check for user: %s " , " Admin " );

So the verified answers are B, C, D, and E .

We want mechanisms that persist data between page loads (i.e., after refresh or navigation), in the browser.

A.  

localStorage

Part of the Web Storage API.

Data persists across page reloads and browser restarts (until explicitly cleared).

Scoped per origin (protocol + host + port).

This is a correct persistent storage API.

B.  

indexedDB

A low-level, client-side NoSQL database in the browser.

Stores large amounts of structured data and persists across reloads and sessions.

This is also a correct persistent API.

C.  

cookies

Small key/value pairs stored by the browser and often sent with HTTP requests.

Can have expiration dates and persist across page loads and sessions.

They are a traditional persistence mechanism in browsers.

So cookies also qualify.

D.  

global variables

Global JS variables exist only for the life of the current page context.

When the page is refreshed or navigated away, they are lost.

They do not persist between page loads.

E.  

IIFEs (Immediately Invoked Function Expressions)

A pattern for creating a new scope, not a persistence mechanism.

Variables inside an IIFE are still lost when the page reloads.

Thus, the three persistent browser APIs are:

localStorage

indexedDB

cookies