The correct answers are C and D .

The statement:

const arr = Array(5).fill(0);

creates an array with 5 elements , and every element is filled with the value 0.

So the array becomes:

[0, 0, 0, 0, 0]

A professional test should verify both important expectations:

arr.length === 5

and:

each element === 0

Option C is correct because it checks every element in the array:

arr.forEach(e = > console.assert(e === 0));

This confirms that each array element was filled with 0.

Option D is correct because it checks the array length:

console.assert(arr.length === 5);

This confirms that the array contains exactly five elements.

Option A is incorrect because the array length is not 0; it is 5.

Option B is incorrect for two reasons. First, arr[5] is outside the valid index range. The valid indexes are:

0, 1, 2, 3, 4

So:

arr[5]

returns:

undefined

Second, arr.length === 0 is false because the length is 5.

Therefore, the verified answers are C and D .

We start with:

let productSKU = ' 8675309 ' ;

The requirement:

Final SKU string:

Length: 19 characters.

Starts with ' sku ' .

Remaining characters are digits padded with zeros on the left (to reach total length).

We can use String.prototype.padStart and String.prototype.padEnd:

str.padStart(targetLength, padString)

If str.length < targetLength, it adds padString to the start until the length is targetLength.

str.padEnd(targetLength, padString)

Similar, but adds padString to the end.

We want a pattern like:

First, pad the numeric part out to a fixed length with zeros.

Then, pad to total length with ' sku ' at the start.

Analyze Option B

productSKU = productSKU.padStart(16, ' 0 ' ).padStart(19, ' sku ' );

Step 1: productSKU.padStart(16, ' 0 ' )

Initial productSKU is ' 8675309 ' (length 7).

After padStart(16, ' 0 ' ), we pad zeros on the left to reach length 16.

We need 16 − 7 = 9 zeros:

Result after step 1:

productSKU === ' 0000000008675309 ' // length 16

Step 2: .padStart(19, ' sku ' )

Now productSKU has length 16.

We call padStart(19, ' sku ' ):

We need 19 − 16 = 3 extra characters.

The pad string ' sku ' is exactly 3 characters, so it is added as-is at the start.

Result after step 2:

productSKU === ' sku0000000008675309 ' // length 19

This satisfies:

Length 19.

Starts with ' sku ' .

Remaining characters are zeros plus the original digits, i.e. a zero-padded numeric section.

While the literal sample sku000000008675309 in the text has a slightly different count of zeros, Option B follows the requirement pattern:

3 characters of ' sku '

Numeric part padded with zeros to make 16 characters total for the numeric part

3 + 16 = 19 total characters

Option B matches the intended logic using padStart and padEnd.

Why the other options are incorrect

Option A:

productSKU = productSKU.padEnd(16, ' 0 ' ).padStart( ' sku ' );

padEnd(16, ' 0 ' ) produces ' 8675309000000000 ' (original number followed by zeros).

padStart( ' sku ' ) is invalid usage:

padStart takes a numeric target length as the first argument, not a string.

Passing ' sku ' as the first argument leads to type coercion that does not achieve the intended behavior.

This will not reliably produce the desired SKU.

Option C:

productSKU = productSKU.padEnd(16, ' 0 ' ).padStart(19, ' sku ' );

First padEnd(16, ' 0 ' ) from ' 8675309 ' gives ' 8675309000000000 ' (length 16, zeros at the end).

Then padStart(19, ' sku ' ) adds 3 chars ' sku ' at the front:

Result: ' sku8675309000000000 ' .

This string starts with ' sku ' , but the zeros are at the end of the digits, not padding the numeric part on the left as desired.

Option D:

productSKU = productSKU.padStart(19, ' 0 ' ).padStart( ' sku ' );

First padStart(19, ' 0 ' ) pads zeros at the left to make the length 19.

Then padStart( ' sku ' ) again incorrectly uses a string where a numeric targetLength is required.

This will not produce the correct SKU format.

Therefore, the only option that correctly uses padStart to create a 16-character zero-padded numeric portion and then a 19-character string starting with ' sku ' is:

Answer: B

References / Study Guide concepts (no links):

String.prototype.padStart(targetLength, padString)

String.prototype.padEnd(targetLength, padString)

String length calculations

Left-padding numeric strings with zeros

Building prefixed identifiers with fixed total length

Node.js provides two built-in modules for creating servers:

http → creates non-secure HTTP servers

https → creates secure HTTPS servers

A secure server requires:

SSL/TLS certificates (key and cert)

The built-in Node.js module designed to handle these: https

Syntax for a secure server:

const https = require( ' https ' );

const fs = require( ' fs ' );

const options = {

key: fs.readFileSync( ' key.pem ' ),

cert: fs.readFileSync( ' cert.pem ' )

};

https.createServer(options, (req, res) = > {

res.write( ' Secure Server ' );

res.end();

}).listen(443);

Evaluation of options:

A is incorrect: No built-in module named secure-server exists.

B is incorrect: tls provides low-level TLS sockets, not HTTP/HTTPS servers.

C is incorrect: http only creates an insecure server.

D is correct: https is the built-in module required for secure web servers.

JavaScript Knowledge References (text-only)

Node.js exposes built-in modules http and https for server creation.

Secure servers require the https module, which supports TLS/SSL.

The tls module is lower-level and not used for full HTTP servers.

==================================================

First, compute sampleText:

let codeName = ' Bond ' ;

let sampleText = `The name is ${codeName}, Jim ${codeName}`;

The template literal evaluates to:

" The name is Bond, Jim Bond "

Now evaluate each statement:

Option A: sampleText.includes( ' Jim ' );

String.prototype.includes(substring) returns true if substring occurs anywhere in the string.

sampleText clearly contains " Jim " ( " The name is Bond, Jim Bond " ).

So this returns true.

Option B: sampleText.includes( ' The ' , 1);

includes(searchString, position) starts searching from the given position index.

" The name is Bond, Jim Bond " has " The " starting at index 0.

Starting search at index 1 means " The " at index 0 is not considered, and there is no second " The " .

So this returns false.

Option C: sampleText.includes( ' Jim ' , 4);

" Jim " appears after " The name is Bond, " which is longer than 4 characters; the index of " Jim " is well past 4.

So when searching from index 4, " Jim " is still found.

This returns true.

Option D: sampleText.indexOf( ' Bond ' ) !== -1;

String.prototype.indexOf(substring) returns:

-1 if the substring is not found,

Otherwise, the starting index of the first occurrence.

" Bond " appears twice in " The name is Bond, Jim Bond " .

So sampleText.indexOf( ' Bond ' ) is some non-negative index (for the first occurrence).

Therefore indexOf( ' Bond ' ) !== -1 is true.

Option E: sampleText.substring( ' Jim ' );

substring expects numeric indexes: substring(startIndex, endIndex?).

If given a string " Jim " as the argument, JavaScript coerces it to a number:

Number( ' Jim ' ) → NaN

NaN for startIndex is treated as 0.

So sampleText.substring( ' Jim ' ) is effectively sampleText.substring(0), which returns the full string " The name is Bond, Jim Bond " .

This is a string , not a boolean. The question asks “which code statements return true?”

This statement returns a string, not the boolean value true.

Thus, the three statements that actually return true (boolean) are:

Answer: A, C, D

Study Guide / Concept References (no links):

Template literals and ${} interpolation

String.prototype.includes(searchString, position?)

String.prototype.indexOf(substring) and checking for !== -1

String.prototype.substring(start, end?) and argument coercion

Boolean vs non-boolean return types in string methods

Requirement:

The message should be displayed only on the first click of the button.

Original behavior:

The handler listen is attached with button.addEventListener( ' click ' , listen);.

That means listen is called on every click until the listener is removed or configured otherwise.

Two correct ways to ensure the listener only fires once:

Use the once option in addEventListener

Remove the event listener after the first run inside the handler

Option C:

On line 06, add an option called once to button.addEventListener().

This means modifying line 06 to:

button.addEventListener( ' click ' , listen, { once: true });

The once: true option tells the browser:

Call the listen function at most once.

After it is called the first time, automatically remove the listener.

So:

First click: alert shows, listener is removed automatically.

Subsequent clicks: no further calls to listen, no alerts.

This satisfies the requirement.

Option D:

On line 04, use button.removeEventListener( ' click ' , listen);

This means updating the handler:

function listen(event) {

alert( ' Hey! I am John Doe ' );

button.removeEventListener( ' click ' , listen);

}

Now:

On the first click, listen is executed:

It shows the alert.

It removes itself from the button’s click listeners.

On subsequent clicks, listen is no longer registered, so nothing happens.

This also satisfies the requirement.

Why A and B are incorrect:

Option A:

On line 04, use event.stopPropagation();

event.stopPropagation() stops the event from bubbling up the DOM tree.

It does not prevent the current listener from being called again in the future.

The click handler will still run on every click; it just prevents other listeners higher in the DOM from receiving the event.

Option B:

On line 02, use event.first to test if it is the first execution.

There is no built-in event.first property in standard DOM events.

This property does not exist and will be undefined.

You would need your own external flag (let hasRun = false;) to track first execution, but that is not what B describes.

Therefore, the two correct modifications are:

Answer: C, D

Study Guide / Concept References (no links):

addEventListener options object: { once: true }

removeEventListener to manually deregister event handlers

Event propagation (event.stopPropagation) vs handler lifecycle

DOM event model and listener registration

ES Modules follow these rules:

Default exports are imported using:

import anyName from ' module '

The name chosen in the import does NOT need to match the exported name.

If a module exports:

export default function printDate() {}

then consuming code should import the function directly:

import printDate from ' /path/DatePrettyPrint.js ' ;

To execute it:

printDate();

Option analysis:

A incorrect: import DatePrettyPrint() is invalid syntax. Also calling printDate() without importing it is incorrect.

B incorrect: A default export imported as DatePrettyPrint gives the function itself, not an object containing methods. You cannot call DatePrettyPrint.printDate().

C incorrect: Imports printDate but then calls DatePrettyPrint.printDate(), which does not exist.

D correct: Correct import of a default-exported function. Correct direct invocation.

JavaScript Knowledge References (text-only)

Default export → imported without braces.

Importing default functions gives a callable function, not an object.

Correct syntax: import identifier from " module " .

==================================================

The File API in browsers provides the FileReader object to read file contents selected from < input type= " file " > .

Important knowledge points:

new FileReader() creates a file-reading object.

.readAsDataURL(file) reads a file and produces a Base64 URL string.

The " load " event fires when the file has finished reading.

reader.result contains the data URL after reading completes.

Therefore, the correct implementation must:

Create a FileReader instance:

const reader = new FileReader();

Call:

reader.readAsDataURL(file);

Use the load event handler to assign the image preview:

preview.src = reader.result;

Option B is the only option that matches valid JavaScript File API usage.

Option A is incorrect because File is not a constructor for reading files.

Option C is incorrect because URL.createObjectURL(file) must be assigned directly as a URL, not used with reader.result.

JavaScript Knowledge References (text-only)

The file-reading interface in browsers is FileReader.

readAsDataURL() loads files as Base64 data URLs.

The load event indicates when the reader has finished and reader.result is available.

==================================================

Synchronous execution order JavaScript executes code in a single thread, following a well-defined order:

All synchronous code runs first, line by line.

Asynchronous callbacks (like those scheduled with setInterval or setTimeout) are placed into the event queue and executed only after the current call stack is empty.

Let’s follow the code step by step:

Line 01:

let total = 10;

total is initialized with the value 10.

Line 02:

const interval = setInterval(() = > {

total++;

clearInterval(interval);

total++;

}, 0);

setInterval schedules the callback function to run repeatedly after a delay of at least 0 milliseconds, but it does not run immediately. The callback is added to the timer queue and will be invoked after the current synchronous script finishes and the event loop gets to process timer callbacks.

At this point, interval holds the interval ID, but the callback has not executed yet.

Line 07:

total++;

This is still synchronous, so it runs before any scheduled callbacks.

total was 10, now it becomes 11.

Line 08:

console.log(total);

At this moment, the interval callback has still not run (because the event loop has not yet processed the timer queue).

So total is 11, and console.log(total); outputs 11.

Therefore, the value printed at line 08 is 11, making option A correct.

What happens after the log (for understanding, not affecting the answer) After the main script finishes, the event loop processes the timer callback for setInterval:

Callback:

() = > {

total++; // from 11 to 12

clearInterval(interval); // cancels further executions

total++; // from 12 to 13

}

So eventually total becomes 13, but this happens after console.log(total) has already executed. Since the question asks specifically for the output at line 08, the asynchronous updates do not change that line’s output.

Why other options are incorrect

Option B (12): This would require the callback to run before the log, which does not happen because asynchronous callbacks are queued and executed after the current stack finishes.

Option C (10): Ignores the total++ on line 07.

Option D (13): This is the final value after the callback finishes, but it occurs after the console.log line executes, not at the time line 08 runs.

JavaScript knowledge references (descriptive, no links):

JavaScript is single-threaded and uses an event loop with a call stack and task queues.

setInterval schedules callbacks to run asynchronously after a minimum delay; the callback never runs before the current synchronous code finishes.

Synchronous statements like total++ on line 07 execute before any queued interval callback.

Comprehensive and Detailed Explanation From JavaScript/Node.js Knowledge:

In a Node.js project that uses package.json, you typically define a " start " script:

{

" scripts " : {

" start " : " node server.js "

}

}

Then you start the app with:

npm start

npm start:

Looks up the " start " script in package.json.

Runs the command defined there (commonly node server.js).

This is the standard way to start a Node.js app with npm-managed dependencies.

Why others are incorrect:

A. node start

Tries to run a file named start with Node; does not use package.json scripts.

C. npm start server.js

npm start does not take the script filename as an argument in this way; it just runs the start script as defined.

D. start server.js

Not an npm or node command; on some shells it just tries to “start” a process but is not the standard Node/npm workflow.

Relevant concepts: package.json, npm scripts, npm start, Node entry file execution.

Animal class:

Has a constructor that sets this.name.

Has a makeSound method that logs a message using this.name.

Dog class:

Extends Animal.

Its constructor calls super(name) to run the parent constructor, which sets this.name.

It overrides makeSound() to log:

console.log(`${this.name} is barking.`);

Instantiation:

let myDog = new Dog( ' Puppy ' );

myDog.makeSound();

new Dog( ' Puppy ' ):

Calls Dog constructor with name = ' Puppy ' .

Inside, super(name) sets this.name = ' Puppy ' in the Animal constructor.

Then this.name = name; in the Dog constructor keeps it as ' Puppy ' .

myDog.makeSound():

Calls the overridden makeSound() in Dog.

Logs: " Puppy is barking. "

No reference errors, no undefined; the output is:

Puppy is barking.

Study Guide Concepts:

ES6 classes and inheritance (extends)

super() in subclass constructors

Method overriding in subclasses

Template literals: `${this.name} ...`