JavaScript-Developer-I Exam Dumps : Salesforce Certified JavaScript Developer (JS-Dev-101)

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 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 .

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.