Free and Premium Salesforce JavaScript-Developer-I Dumps Questions Answers

Definitions:

False negative → The test reports a failure even though the feature actually works.

False positive → The test reports success when it should not.

True positive → Correctly identifies something is working.

True negative → Correctly identifies something is not working.

In this scenario:

The checkout button does exist , so the feature works.

The test fails incorrectly , because it is checking for the wrong selector.

That is the definition of a false negative .

JavaScript Knowledge References (text-only)

Test outcome classification: false negative = feature works but test fails.

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The key line is:

for (let something of obj) {

In JavaScript:

for...of is used to iterate over iterable objects, such as:

Arrays

Strings

Maps

Sets

Other objects that implement a [Symbol.iterator] method.

Plain JavaScript objects created with object literal {} are not iterable by default . They do not have [Symbol.iterator], so using for...of directly on them causes a runtime error.

Specifically:

for (let something of obj) { ... }

will throw a TypeError similar to:

obj is not iterable

Therefore, the loop body never executes, and console.log(output); is never reached without an error.

Why other options are incorrect:

B. [1, 2]

To get [1, 2], you could use Object.values(obj) and iterate that array.

But here, for...of obj never yields values because it throws an error.

C. [ " foo " , " bar " ]

To get property names, you could use Object.keys(obj) with for...of.

Again, the code does not do that; it incorrectly tries to iterate the object directly.

D. [ " foo:1 " , " bar:2 " ]

You would need both keys and values, combining them manually.

The given code does not implement such logic and fails before pushing anything into output.

Hence, the correct answer is:

Answer: A

Study Guide / Concept References (no links):

Difference between for...of and for...in

Iterables in JavaScript and [Symbol.iterator]

Plain objects {} are not iterable by default

Correct patterns to iterate object keys/values (Object.keys, Object.values, Object.entries)

Execution order:

Top-level code runs synchronously:

Line 14: console.log(4); → logs 4.

Line 15: callDelay(); is called.

Inside callDelay:

Line 9: console.log(2); → logs 2.

Line 10: await delay(1000);:

Calls delay(1000).

Inside delay(1000):

Line 3: console.log(1); → logs 1.

Line 4: setTimeout(resolve, delay); schedules resolve in 1000 ms.

delay returns a pending Promise. await pauses callDelay here and returns control to the event loop.

Back to top-level:

Line 16: console.log(5); → logs 5.

So synchronous log sequence is: 4, 2, 1, 5.

After ~1000 ms:

The setTimeout in delay resolves the Promise.

The await in callDelay resumes.

Line 11: console.log(3); → logs 3.

Final log order: 4 2 1 5 3.

Both A and B show the same sequence; one must be chosen, so A is correct.

Concepts: async/await flow, Promise resolution timing, event loop, and ordering of synchronous vs timer callbacks.

The correct answer is C .

The browser provides the History API through:

window.history

To add a new entry to the browser’s session history without refreshing the page, JavaScript uses:

window.history.pushState(state, title, url);

So the valid statement is:

window.history.pushState(newStateObject, ' ' , null);

This updates the browser history stack without forcing a full page reload. It is commonly used in single-page applications when changing views or routes dynamically.

The method accepts three arguments:

window.history.pushState(stateObject, title, url);

stateObject stores custom data associated with the history entry.

title is usually passed as an empty string because many browsers ignore it.

url optionally changes the displayed URL. Passing null means no new URL is provided.

Option A is incorrect because:

window.customHistory

is not the standard browser History API object.

Option B is incorrect because:

createState()

is not a valid History API method.

Option D is incorrect because:

updateState()

is not a valid History API method.

The correct browser API method is:

window.history.pushState()

Therefore, the verified answer is C .

Expression:

true + ' 13 ' + NaN

The + operator is left-associative, so evaluation order:

true + ' 13 '

When one operand is a string, + performs string concatenation.

true is converted to string ' true ' .

' true ' + ' 13 ' → ' true13 ' .

Result from step 1 with NaN:

' true13 ' + NaN

Again, one operand is a string, so concatenation.

NaN is converted to string ' NaN ' .

' true13 ' + ' NaN ' → ' true13NaN ' .

Final value: ' true13NaN ' .

So A is correct.

Why others are wrong:

B: ' 113NaN ' would require true to coerce to 1 first and no string to be present, which is not the case because ' 13 ' forces string concatenation.

C: 14 would require pure numeric addition, which is not the case once a string is involved.

D: ' true13 ' ignores the final + NaN part.

Concepts: type coercion with +, boolean to string, NaN to string, left-associative evaluation.

The correct answer is C .

When getAvailability(item) returns true, the code inside the if block executes:

var msg = " Username available " ;

return msg;

The variable msg receives the string value:

" Username available "

Then that same value is returned from the function.

The key point is that var is function-scoped, not block-scoped. So msg belongs to the function scope of getAvailabilityMessage(). However, because the return msg; statement is inside the same if block, the function immediately returns the assigned string when the username is available.

Option A is incorrect because msg is defined before it is returned.

Option B is incorrect because " newUserName " is not assigned or returned anywhere in the function.

Option D would only happen if getAvailability(item) returned false, because then the function would finish without an explicit return value.

For the available username scenario, the verified answer is C .

console.assert(condition, message?) logs an assertion error if condition is falsy.

To log an error when number + 2 === 0 is false, use:

console.assert(number + 2 === 0);

Other options are invalid or do not behave as described: console.error always logs, assert alone is not a built-in browser global, and console.classy doesn’t exist.

Node.js includes a built-in command-line (CLI) debugger . To use it directly in the terminal, the standard command is:

node inspect server.js

This:

Starts server.js under the Node.js inspector.

Opens the CLI debugger right in the terminal window where you ran the command.

Lets you interactively:

Step through code

Set breakpoints

Inspect variables

Continue execution, etc.

Why B is correct:

Option B (corrected to node inspect server.js) is exactly the standard Node.js command to run a script under the CLI debugger in the current terminal.

It does not rely on any external GUI tools.

You stay entirely in the terminal to debug.

Why the other options are incorrect:

A. node start inspect server.js

There is no start subcommand like this in standard Node.js CLI.

This is not a valid Node.js debugging command.

C. node server.js --inspect

This starts Node.js with the Inspector protocol enabled and is typically used to connect external tools like Chrome DevTools or VS Code.

It does not open the CLI debugger in the current terminal. Instead, it opens a debugging port that other tools attach to.

The question specifically says “only using the terminal” and “open the CLI debugger in their current terminal window”, which points to node inspect, not --inspect.

D. node -i server.js

-i starts Node in interactive REPL mode , optionally after running a script.

This is for an interactive shell, not the Node debugger.

It does not provide breakpoint/step/next/continue debugging features like the CLI debugger.

Therefore, the only option that opens the Node.js CLI debugger in the current terminal is:

Answer: B

JavaScript / Node.js knowledge / Study Guide references (concept names only, no links):

Node.js CLI debugger: node inspect < script >

Node.js inspector protocol: node --inspect

Difference between CLI debugger and DevTools-based debugging

Node.js command-line options and subcommands

The verified answer is A .

This constructor function runs when new Person() is called:

function Person() {

this.firstName = " John " ;

}

So this line:

const myFather = new Person();

creates an object like this:

{

firstName: " John "

}

Then the prototype is assigned a method named job:

Person.prototype = {

job: x = > " Developer "

};

Because myFather is created from Person, it can access properties and methods from Person.prototype.

So:

myFather.firstName

returns:

" John "

And:

myFather.job()

returns:

" Developer "

Therefore:

const result = myFather.firstName + " " + myFather.job();

becomes:

const result = " John " + " " + " Developer " ;

Final value:

" John Developer "

Option B is incorrect because job() returns " Developer " , not undefined.

Option C is incorrect because job exists on Person.prototype, so it is callable.

Option D is incorrect because firstName is assigned inside the constructor.

Therefore, the verified answer is A .

New behavior: sum3 now returns the sum of all elements .

Line 01: sum3([1, 2, 3]) → 1 + 2 + 3 = 6

Assertion on line 02: res === 6 → passes.

Line 04: sum3([1, 2, 3, 4]) → 1 + 2 + 3 + 4 = 10

Assertion on line 05: res === 6 → 10 === 6 is false, so the assertion fails.

So:

Line 02 assertion passes → D.

Line 05 assertion fails → C.

import * as lib from ' ... ' imports all named exports from the module into the namespace object lib.

You then call:

lib.foo();

lib.bar();

Option D correctly imports only foo and bar, not every function. The question explicitly says “import every function… and then call foo and bar”, so A best matches.

Options B and C are invalid syntax or reference the wrong identifier.

JSON.stringify() applies the following rules:

String objects (new String( ' false ' )) Are converted to their primitive string values . So:

new String( " false " ) → " false "

Boolean objects (new Boolean(false)) Convert to their primitive boolean value :

new Boolean(false) → false

Undefined values inside arrays According to the JSON specification, undefined becomes null when stringifying an array:

JSON.stringify([undefined]) → " [null] "

Therefore, the array becomes:

[ " false " , false, null]

And JSON.stringify wraps it in quotes:

' [ " false " , false, null] '

This is exactly option A.

JavaScript Knowledge References (text-only)

Object wrappers (String, Boolean) are converted to primitives during JSON serialization.

undefined becomes null inside arrays when stringified.

JSON.stringify() follows the JSON data-model rules strictly.

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Event-driven Node-style APIs expose events via .on(eventName, handler).

To listen for error events:

server.on( ' error ' , (error) = > {

console.log( ' ERROR ' , error);

});

A and B assume methods .error or .catch that don’t exist on typical event emitters.

C only catches synchronous errors from server.start(), not async event-based errors.

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.

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Key details:

var has function scope , not block scope.

Declaration var msg is hoisted to the top of the function, but initialization only happens if the if condition is true.

Effectively, the function behaves like:

function getAvailableilityMessage(item) {

var msg; // hoisted declaration

if (getAvailableility(item)) {

msg = " Username available " ;

}

return msg;

}

Now, given:

getAvailableility( " newUserName " ) returns false.

Execution:

The if condition is false, so the body does not execute.

Therefore msg is declared but never assigned .

In JavaScript, an uninitialized variable that has been declared with var has the value undefined.

Thus:

return msg; // returns undefined

Why other options are wrong:

A: " newUserName " – msg never receives the parameter value; it ' s only set to " Username available " inside the if, which does not run.

B: " msg is not defined " – That kind of error occurs if msg were never declared. Here it is declared via var, so it is defined but undefined.

D: " Username available " – This would require the if branch to run, which it does not when getAvailableility(...) is false.

So the return value is:

undefined

Study Guide Concepts:

var hoisting and function scope

Uninitialized variables default to undefined

Control flow and conditional initialization

execute() returns a Promise that immediately calls reject(). So promise starts in a rejected state.

When a Promise is rejected and you chain .then() calls without rejection handlers, all those .then() callbacks are skipped until a .catch() is encountered:

promise

then(...) // skipped

then(...) // skipped

then(...) // skipped

catch(...) // executed

then(...); // executed after catch

Execution:

.then(() = > console.log( ' Resolved1 ' )) is skipped.

.then(() = > console.log( ' Resolved2 ' )) is skipped.

.then(() = > console.log( ' Resolved3 ' )) is skipped.

.catch(() = > console.log( ' Rejected ' )) runs and logs Rejected.

The .catch() returns a resolved Promise (no explicit return, so undefined), so the next .then() runs:

.then(() = > console.log( ' Resolved4 ' )) logs Resolved4.

Final output:

Rejected

Resolved4

This matches option D.

The code:

let timerId = setInterval(timedFunction, 1000);

setInterval schedules timedFunction to run every 1000 ms.

It returns an interval ID (here stored in timerId), which is used to cancel the interval later.

To cancel:

Use clearInterval(timerId);

This is the standard browser (and Node.js) API:

let id = setInterval(fn, delay);

clearInterval(id); stops future executions of that interval.

Check other options:

B. removeInterval(timerId);

There is no removeInterval function in the standard JavaScript timer API.

C. removeInterval(timedFunction);

Again, no such function; and timers are cancelled by ID, not by the callback function reference.

D. clearInterval(timedFunction);

clearInterval expects the ID returned by setInterval, not the callback function.

Passing the function does not cancel the timer.

Therefore, the correct statement is:

Answer: A

Study Guide / Concept References (no links):

Timer APIs: setInterval and clearInterval

Relationship between timer ID and cancellation

Difference between interval ID and callback function

Basic async timing patterns in JavaScript

Behavior of Promise.prototype.finally:

.finally(handler) registers a callback that runs when the promise is settled , meaning:

Either fulfilled (resolved) , or

rejected .

Important points:

The finally callback does not receive the promise’s value or error (unlike then and catch).

It is executed after the promise is settled, but before the resolution value or rejection reason is passed further down the chain.

It runs in both success and failure paths.

In the given code:

The promise may either:

Call reject( ' fraction > 0.5, ' + fraction) if fraction > 0.5, or

Call resolve(fraction) otherwise.

In both cases:

If it resolves , .then(() = > console.log( ' resolved ' )) runs, and then .finally(...) is executed.

If it rejects , .catch((error) = > console.error(error)) runs, and then .finally(...) is executed.

So .finally runs:

Not just “when rejected”.

Not just “when resolved”.

But whenever the promise is resolved or rejected .

Therefore, the correct choice is:

D. When resolved or rejected .

When pet1 = new Pet(); is created:

Inside Pet constructor:

Animal.call(this, size, type);

this.size = size;

this.name = name;

this.owner = owner;

Animal.call(this, size, type):

Sets this.type = type || ' Animal ' → ' Animal ' (because type is undefined).

Sets this.canTalk = false.

Then this.size, this.name, this.owner are set (to undefined since no args passed), but they do exist as properties .

So as own properties, pet1 has: type, canTalk, size, name, owner.

speak is defined on Animal.prototype, so pet1.speak exists by inheritance, but is not an own data property created in the constructor.

From the listed options, three important properties directly set by constructor logic and clearly used in behavior are:

canTalk

name

type

Thus, C, D, E.

The syntax:

import printPrice from ' module ' ;

means the module must export its function as a default export :

export default function printPrice() { ... }

Why the others are wrong:

Named exports require curly braces:

import { printPrice } from ' module ' ;

“all export” and “multi export” are not JavaScript terms.

Therefore, printPrice must be the default export .

JavaScript Knowledge References (text-only)

Default imports use: import name from ' module ' .

Named imports require braces: import { name } from ' module ' .

Comprehensive and Detailed Explanation:

Errors thrown inside setTimeout callbacks occur asynchronously, in a different tick of the event loop. A try...catch around setTimeout itself (as in D) cannot catch errors thrown later in the scheduled callback.

To catch errors from countSheep() when it’s called asynchronously, the try...catch must wrap the call inside the timeout callback:

setTimeout(function() {

try {

countSheep();

} catch (e) {

handleError(e);

}

}, 1000);

B uses finally incorrectly and references e out of scope.

C is not valid JavaScript syntax.

D’s catch can only handle synchronous errors thrown before setTimeout returns, not those thrown inside the callback.

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 " .

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Browsers often cache JavaScript, CSS, and HTML. This means:

The developer may be running with the latest version (often with cache disabled in DevTools).

The tester may still be loading an older, cached version of the page where the background-change logic does not exist.

To ensure they are actually testing the latest deployed code:

Disabling cache (A) in the tester’s browser (usually via DevTools → Network → “Disable cache”) forces fresh loading of all resources on each refresh.

Clearing cache (C) removes older resources from the browser so the next load fetches fresh files from the server.

Options B and D do not directly help verify the tester is using the latest code:

B checks the developer’s own browser, which is not the environment showing the problem.

D suggests reworking the code before confirming whether the tester is actually loading the correct version, which is premature.

So the two actions that help produce accurate testing results are A and C.

From earlier pattern (cars/cats race):

One promise resolves the fastest with " Car 2 completed " (or analogous " Cat 2 completes " ).

Promise.race resolves with the first settled promise’s value.

In .then, value is " Car 2 completed " and:

let result = `${value} the race.`;

// " Car 2 completed the race. "

Thus result is " Car 2 completed the race. " → option A.

Evaluate each test:

A. sum3([1, ' 2 ' ])

Array length is 2 → line 4: arr[0] + arr[1] → 1 + ' 2 ' → ' 12 ' (string).

Assertion: ' 12 ' == 12 is true (type coercion). However, this “test” is not logically correct: a numeric sum function should not be expected to return ' 12 ' as a string. It passes only because of weak equality coercion, so it is not a good/valid test of correct behavior.

B. sum3([ ' hello ' , 2, 3, 4])

Length ≥ 3 → line 5: ' hello ' + 2 + 3 → ' hello2 ' + 3 → ' hello23 ' .

' hello23 ' === NaN is always false because NaN is never equal to anything, not even itself. This assertion fails and also misunderstands how NaN comparisons work.

C. sum3([-3, 2])

Length 2 → -3 + 2 = -1.

Assertion: -1 === -1 → true. This is a correct and meaningful test.

D. sum3([0])

Length 1 → returns arr[0] → 0.

Assertion: 0 === 0 → true. Also a correct and meaningful test.

Therefore, the valid and logically correct tests here are C and D.

The correct answer is A .

This object uses a getter :

get fullName() {

return this.firstName + ' ' + this.lastName;

}

A getter looks like a method when it is defined, but it is accessed like a normal property.

So the correct access syntax is:

dog.fullName

That returns:

" Beau Boo "

The important distinction is:

dog.fullName

not:

dog.fullName()

Because fullName is a getter property, not a regular function property.

Option B is incorrect because calling dog.fullName() tries to call the returned string as a function. Since " Beau Boo " is not a function, that would cause a TypeError.

Option C is incorrect because there is no get object inside dog.

Option D is incorrect because there is no function object inside dog, and getters are not accessed that way.

Therefore, the verified answer is A .

This question focuses on the typeof operator and how JavaScript represents the type of the value null.

Declaration on line 1:

let x = null;

Here:

x is explicitly assigned the value null.

In JavaScript, null is a special primitive value that represents “no value” or “empty value”.

Line 2:

console.log(typeof x);

The typeof operator returns a string indicating the type of the operand. For example:

typeof 1 returns " number "

typeof " hello " returns " string "

typeof true returns " boolean "

typeof undefined returns " undefined "

typeof {} returns " object "

typeof [] returns " object " (arrays are objects)

typeof function() {} returns " function "

For null, due to an early design decision in JavaScript, the result is:

typeof null === " object "

This is a known historical quirk of the language:

Although null is a primitive and conceptually means “no object”, typeof null returns the string " object " .

Therefore, typeof x when x is null evaluates to " object " .

So on line 2, the value printed is:

" object "

This matches option A.

The incorrect options are:

B. " undefined " : would be typeof x if x were undefined, not null.

C. " x " : typeof returns a string describing the type of the value, not the variable name.

D. " null " : although intuitive, JavaScript does not return " null " for typeof null; it returns " object " instead.

Therefore, the correct answer is:

Answer: A

JavaScript knowledge / study guide reference concepts:

typeof operator and its return values

Primitive types in JavaScript (null, undefined, number, string, boolean, symbol, bigint)

Historical behavior: typeof null returning " object "

Difference between null and undefined in JavaScript

We have a ternary:

account.style.display = accountName.includes(parsedSearchString)

? /* if true */

/* if false */;

Requirement:

If the account matches the search string → show it.

If it does not match → hide it.

For display:

Show: ' block ' (or similar visible value).

Hide: ' none ' .

So we want:

account.style.display = accountName.includes(parsedSearchString)

? ' block '

' none ' ;

That corresponds to option A.

Why others are wrong:

B, C use values suitable for visibility, not display.

D ( ' none ' : ' block ' ) inverts the logic, hiding matches and showing non-matches.

We must understand pass-by-value for primitives in JavaScript.

Initial values:

let a = 10;

let b = a; // b gets a copy of the value 10

So:

a is 10

b is 10 (independent copy)

Function call:

changeValue(b);

Function definition:

function changeValue(param) {

param = 5;

}

param receives the value of b, which is 10.

Inside the function, param is a local variable .

param = 5; changes only this local copy.

It does not affect b outside the function.

After the function call:

a is still 10.

b is still 10.

Result:

const result = a + ' - ' + b;

a is 10.

b is 10.

String concatenation: ' 10 - 10 ' .

So result is:

" 10 - 10 "

Therefore, the correct option is:

Answer: D

Study Guide Concepts:

Primitive values (numbers, strings, booleans) are passed by value

Function parameters as local variables

String concatenation with +

Difference between mutating references vs primitives

userInformation is a plain JavaScript object:

{

id: " user-01 " ,

email: " user01@universalcontainers.demo " ,

age: 25

}

You can access object properties in two standard ways:

Dot notation : object.propertyName

Bracket notation : object[ ' propertyName ' ]

Apply to each option:

A. userInformation.email

Correct dot notation; accesses " user01@universalcontainers.demo " .

B. userInformation.get( " email " )

.get() is a method on Map instances, not on plain objects.

A regular object does not have a .get method; this would be TypeError.

C. userInformation[ " email " ]

Correct bracket notation; string " email " is used as the property key.

Returns " user01@universalcontainers.demo " .

D. userInformation[email]

Here email is treated as a variable, not a string literal.

Unless there is a variable named email defined with a value matching a property key, this will either:

Throw a ReferenceError (if email is not defined), or

Use the value of email as a computed key (not what is intended here).

It is not the correct way to access the " email " property literal.

Therefore, the correct ways are:

Answer: A, C

Relevant concepts: object property access (. vs []), plain objects vs Map, literal property names vs computed property names.

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

The correct answer is B because the JavaScript browser console allows developers to interact with the current web page using JavaScript commands. Through the console, you can access the document object, inspect DOM elements, read their properties, and modify the structure or content of the page.

For example:

document.body.style.backgroundColor = " lightblue " ;

This changes the page’s background color.

Another example:

document.querySelector( " h1 " ).textContent = " Updated Heading " ;

This changes the text of the first < h1 > element on the page.

The DOM , or Document Object Model, is the browser’s JavaScript representation of the HTML page. Since the console runs JavaScript in the context of the current page, it can be used to inspect and modify DOM elements directly.

Why the other options are incorrect:

A is not the best answer because although you can type general JavaScript expressions in the console, the browser console is mainly connected to the current page’s execution environment. The question is asking about practical browser-console actions related to a page.

C is incorrect because performance reports are usually generated through tools such as the Performance panel or Lighthouse in browser developer tools, not directly through the JavaScript console.

D is incorrect because the console can modify the DOM and runtime values, but it does not permanently change the original JavaScript source code of the page. Any changes made through the console are temporary and disappear when the page reloads.

E is incorrect because security-protected cookies, such as HttpOnly cookies, cannot be viewed or changed using JavaScript. This is an intentional browser security feature that prevents client-side scripts from accessing sensitive cookie data.

Therefore, the best verified answer is B .

Evaluate each option:

A. Arguments for .then() are optional.

This is correct.

then() has the signature:

promise.then(onFulfilled?, onRejected?)

Both arguments (onFulfilled and onRejected) are optional.

If a callback is not supplied, JavaScript provides a default pass-through handler.

B. .then() cannot be added after a catch.

Incorrect.

Promises support chaining in any order:

promise

catch(...)

then(...);

After a catch, the chain continues normally.

C. .then() manipulates and returns the original promise.

Incorrect.

then() always returns a new promise , not the original one.

This is fundamental to promise chaining behavior.

D. Returning values in .then() is not necessary.

Incorrect.

If you want the next .then() in the chain to receive a value, the current .then() must explicitly return it:

then(value = > {

return value * 2; // passes to next .then()

})

If nothing is returned, the next .then() receives undefined.

Why A is correct

It is the only statement that accurately describes built-in Promise behavior:

then() accepts optional arguments.

JavaScript Knowledge References (text-only)

.then(onFulfilled?, onRejected?) accepts optional handlers.

Promise chaining creates new promises for each .then().

catch() can be followed by additional .then() calls.

Returning inside .then() passes values to the next step in the chain.

console.log() in browser-side JavaScript writes output to the browser’s JavaScript console , which is available in the browser’s Developer Tools.

In a typical browser (Chrome, Firefox, Edge, etc.), you open DevTools and go to the Console tab.

Any console.log( " Page has loaded! " ); executed in page JavaScript will appear there.

Why A is correct:

The function onLoad is a client-side function (runs in the browser).

When it executes, the console.log call goes to the browser’s JavaScript console , not the server.

Why the others are incorrect:

B. On the terminal console running the web server

That console shows logs from the server-side runtime (e.g., Node.js logs).

This code is clearly browser-side JavaScript (no Node.js or server context shown).

Therefore, the output does not appear in the terminal.

C. In the browser performance tools log

Performance tools (Timeline, Performance tab, etc.) show metrics about rendering, CPU time, network, etc., not generic console.log messages.

console.log messages appear in the Console tab, not in performance logs.

D. On the webpage console log

There is no built-in concept of a “webpage console log” UI rendered on the page itself by default.

Unless you explicitly code something to display logs in the DOM, console.log output is not visible on the page, only in Developer Tools.

Therefore, the correct place to see that log is:

Answer: A

JavaScript knowledge / Study Guide references (concept names only, no links):

Browser Developer Tools – Console tab

console.log() in client-side JavaScript

Difference between client-side logs and server-side logs

document.querySelector( ' #row-as ' ) returns the single element with id row-as.

That element has a classList property with add, remove, etc.

Correct usage:

document.querySelector( ' #row-as ' ).classList.add( ' priority-account ' );

Why others are wrong:

A: querySelectorAll returns a NodeList, not a single element, so it does not have a classList property.

C: DOM elements do not have a classes array or push; they have classList.

D: document.getElementById( ' row-as ' ) is fine to get the element, but there is no addClass method in standard DOM; that’s a jQuery-style API, not vanilla JS.

The goal:

" Temporarily and quickly remove them. "

The fastest way is to run a script in the browser console that removes all such elements:

document.querySelectorAll( ' .ad-library-item ' ).forEach(el = > el.remove());

This immediately removes all 50+ elements and requires no page reload.

Option analysis:

A & B : Preventing load events is unreliable and does not remove already-created DOM nodes.

C : Correct—console code can remove all matching DOM elements instantly.

D : Possible but extremely slow; removing 50+ elements one by one in the inspector is not “quick.”

Therefore, C is the best answer.

JavaScript Knowledge References (text-only)

The browser console can run arbitrary JavaScript that manipulates the DOM.

document.querySelectorAll() returns all matching DOM nodes.

Nodes can be removed using .remove().

If the dependency was added as a dev dependency (yarn add --dev), it goes into devDependencies.

When NODE_ENV=production, Yarn (and npm) typically skip devDependencies on install.

Thus the package doesn’t get installed for other team members in a production environment.

YARN_ENV is not a standard variable, --save is npm syntax (and Yarn saves by default), and --add is not how Yarn works (the command itself is yarn add).

Requirement:

getNextValue() should run only if handleObjectValue(x) does not throw an error.

If an error occurs, handleError(error) should run, and getNextValue() should be skipped.

Option B:

try {

handleObjectValue(x);

getNextValue();

} catch (error) {

handleError(error);

}

Behavior:

If handleObjectValue(x) succeeds (no error):

Execution continues to getNextValue();.

If handleObjectValue(x) throws:

Control jumps directly to catch, getNextValue() is skipped.

handleError(error); is called.

This matches the requirement perfectly.

Why others are incorrect:

A: } then { is invalid JavaScript syntax.

C:

try {

handleObjectValue(x);

} catch (error) {

handleError(error);

}

getNextValue();

getNextValue() is called after the try...catch regardless of whether an error occurred. Not acceptable.

D: finally always runs:

try {

handleObjectValue(x);

} catch (error) {

handleError(error);

} finally {

getNextValue();

}

getNextValue() will execute in both success and error cases.

Therefore, the correct approach is B.

Concepts: try/catch control flow, finally semantics, placing code inside vs outside try/catch blocks.

The question is about:

Web frameworks that run on Node.js

Used to build servers and APIs

With established communities.

From the given options:

Angular:

A front-end framework running in the browser, not a Node.js server framework.

Gatsby:

A React-based static site generator; uses Node tooling but is not primarily a Node server framework.

Next / Next.js:

Server-side rendering / full-stack frameworks built on Node.js and React.

Used to create both server-rendered pages and APIs.

They have active communities and are “seasoned” compared to a hypothetical Minimalist.js.

Although typical Node back-end frameworks would include Express.js, Koa, or NestJS, given the options provided, the best fits for server-side frameworks with Node.js and an ecosystem are:

Next (interpreted as Next.js)

Next.js

Thus, the correct pair from the list is B and D.

Concepts: Node.js web frameworks, server-side rendering, community-backed frameworks vs minimal/new frameworks.

fullName is defined as a getter :

get fullName() { ... }

Getters are accessed like properties , not like functions.

So:

cat.fullName; // " Fancy Whiskers "

No parentheses.

Why others are wrong:

A: cat.fullName() tries to call the returned string as a function.

B and C: These properties (get, function) do not exist; they are misinterpretations of syntax.

We already know NaN is special: it is not equal to itself.

Check each:

A. value === Number.NaN

Number.NaN is NaN.

NaN === NaN is always false.

This will never be true; cannot reliably detect NaN.

B. value == NaN

NaN == NaN is also always false.

Again, this never detects NaN.

C. isNaN(value)

Global isNaN converts its argument to a number and then checks if the result is NaN.

This can detect NaN, but it may also return true for non-number values that coerce to NaN, such as isNaN( ' foo ' ).

Regardless, it is a standard way to detect if a value is “NaN-like” in JavaScript.

D. Object.is(value, NaN)

Object.is(NaN, NaN) returns true.

This is a strict way to detect a value that is exactly NaN (no coercion).

Therefore, among the given choices, the two viable ways to detect NaN are:

isNaN(value)

Object.is(value, NaN)

In JavaScript, NaN has some special properties:

NaN is not equal to anything, including itself.

Equality operators (==, ===) do not work for detecting NaN.

Check each option:

A. value === Number.NaN

Number.NaN is just NaN.

But NaN === NaN is always false.

So this expression is never true and cannot be used to detect NaN.

B. value == NaN

Same issue. NaN == NaN is always false.

So this also never detects NaN.

C. Object.is(value, NaN)

Object.is is a more precise equality comparison method.

It treats NaN as equal to NaN: Object.is(NaN, NaN) is true.

So Object.is(value, NaN) is a valid way to detect NaN.

D. value !== value

Because NaN is the only JavaScript value that is not equal to itself , value !== value is true only when value is NaN.

This is a classic trick for NaN detection.

E. Number.isNaN(value)

Number.isNaN is the recommended modern way to check if a value is NaN without coercion .

It returns true only if value is actually the number NaN.

Therefore, the three correct ways are:

Object.is(value, NaN)

value !== value

Number.isNaN(value)

In Node.js:

__filename is the absolute path to the current file (including file name).

__dirname is the absolute path to the directory that contains the current file.

window.location is a browser-only global, not available in Node.js.

this.path is not a standard Node.js global for path information.

The requirement is:

“the folder location that the code executes from.”

That is exactly what __dirname provides.

So the correct choice is __dirname.

Concepts: Node.js globals, __filename, __dirname, Node vs browser environment.

The correct answers are A and C because both use named exports for foo and bar.

A module can export multiple values by name:

export { foo, bar };

This allows another file to import them like this:

import { foo, bar } from ' ./utils.js ' ;

Option A is correct because it defines both functions locally and exports both of them as named exports.

const foo = () = > { return ' foo ' ; };

const bar = () = > { return ' bar ' ; };

export { foo, bar };

Option C is also correct after correcting the typing issue so that both foo and bar are imported first:

import { foo, bar } from " ./helpers/utils.js " ;

export { foo, bar };

This is called re-exporting. The module imports foo and bar from another module, then exports them again from utils.js.

Option B is not the best answer for named access because it exports one default object:

export default { foo, bar };

That would require a default import first:

import utils from ' ./utils.js ' ;

utils.foo();

utils.bar();

It does not directly support named imports in the same way as:

import { foo, bar } from ' ./utils.js ' ;

Option D exports a default class. Its foo() and bar() are class instance methods, not named exported functions. It would require usage like:

import Utils from ' ./utils.js ' ;

const utils = new Utils();

utils.foo();

utils.bar();

So for direct multiple function exports, the correct implementations are A and C .