Salesforce JavaScript-Developer-I - Salesforce Certified JavaScript Developer (JS-Dev-101)

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.

Comprehensive and Detailed Explanation:

Assuming SaleItem inherits from Item via prototype (e.g. SaleItem.prototype = Object.create(Item.prototype)):

Lines 01–02: create regItem and saleItem.

Line 03: define Item.prototype.description.

Now both regItem and saleItem (via inheritance) have a description method from Item.prototype.

Line 04: regItem.description() → ' This is a Scarf ' .

Line 05: saleItem.description() → ' This is a Shirt ' (same method, but this.name is ' Shirt ' ).

Line 07: SaleItem.prototype.description = ... overrides description only for SaleItem instances going forward.

If we imagine calling regItem.description() and saleItem.description() again after line 07:

regItem.description() still uses Item.prototype.description → ' This is a Scarf ' .

saleItem.description() now uses SaleItem.prototype.description → ' This is a discounted Shirt ' .

Those four lines correspond to option B.

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.

Facts about JavaScript Promises:

runParallel() is declared async, which means it always returns a Promise .

Promises are consumed using .then(), .catch(), and .finally().

There is no .done() method in native JavaScript Promises.

The async keyword cannot be placed before a function call (option A is invalid syntax).

Analysis of each option:

A. async runParallel().then(data);

Invalid syntax. async cannot prefix an expression.

B. Valid. Calls the function and attaches a .then() handler.

C. Invalid. .done() is not part of JavaScript Promise API.

D. Valid. Calls runParallel() and chains .then().

Therefore the correct answers are B and D.

JavaScript Knowledge References (text-only)

async functions return Promises.

Promises use .then() to retrieve resolved values.

.done() is not part of the standard Promise interface.

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At line 03, the developer assigns:

Item.prototype.description = function() { return ' This is a ' + this.name; }

This affects all objects whose prototype chain includes Item.prototype .

regItem inherits from Item → gets this method.

saleItem, as an instance of SaleItem, also inherits Item.prototype (since SaleItem uses prototype inheritance from Item), so it also has this method at this moment.

Outputs at lines 04 and 05:

regItem.description() → " This is a Scarf "

saleItem.description() → " This is a Shirt "

At line 07, the developer overrides the method on SaleItem.prototype :

SaleItem.prototype.description = function() {

return ' This is a discounted ' + this.name;

}

From this point:

regItem still uses the Item.prototype version

saleItem uses the overridden SaleItem.prototype version

Outputs at lines 08 and 09:

regItem.description() → " This is a Scarf "

saleItem.description() → " This is a discounted Shirt "

Combining all results:

This is a Scarf

This is a Shirt

This is a Scarf

This is a discounted Shirt

This matches option B .

JavaScript Knowledge References (text-only)

Objects created from constructor functions use prototype chaining.

Overriding a subclass prototype method does not affect the parent class prototype.

Instances inherit the most specific version of the method on their prototype chain.

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Comprehensive and Detailed Explanation:

The loop removes every 4:

Start: [1, 2, 3, 4, 4, 5, 4, 4]

i=0 → 1 (no change)

i=1 → 2 (no change)

i=2 → 3 (no change)

i=3 → 4 → splice removes index 3 → [1,2,3,4,5,4,4], then i-- → 2

Next loop, i=3 → 4 again → splice → [1,2,3,5,4,4], i-- → 2

i=3 → 5 (no change)

i=4 → 4 → splice → [1,2,3,5,4] , i-- → 3

i=4 → 4 → splice → [1,2,3,5], i-- → 3

Next i=4, array.length is 4 → loop ends.

All 4s removed, final array: [1, 2, 3, 5].

The correct answers are A, B, and C .

The original variable name appears to contain a typing error. The variable should be used consistently as sampleText:

let sampleText = " The quick brown fox jumps " ;

A is correct because includes() checks whether a string contains a specific substring and returns a Boolean value:

sampleText.includes( ' fox ' );

Since " fox " exists inside " The quick brown fox jumps " , this returns:

true

B is correct after correcting the typing error. The correct expression is:

sampleText.indexOf( ' quick ' ) > -1;

indexOf() returns the index position where the substring is found. If the substring is not found, it returns -1.

Since " quick " exists in the string, sampleText.indexOf( ' quick ' ) returns a value greater than -1, so the expression returns:

true

C is correct after correcting the missing quotation marks and adding a Boolean comparison:

sampleText.indexOf( ' fox ' ) !== -1;

The substring " fox " exists in the string, so indexOf( ' fox ' ) does not return -1. Therefore, the expression returns:

true

D is incorrect because the method name is typed incorrectly. JavaScript string has includes(), not include().

Incorrect:

sampleText.include( ' fox ' )

Correct:

sampleText.includes( ' fox ' )

E is incorrect because JavaScript string matching is case-sensitive:

sampleText.indexOf( ' Quick ' ) !== -1;

The string contains " quick " with a lowercase q, not " Quick " with an uppercase Q, so this returns:

false

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

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.

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.

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.