Get Salesforce JS-Dev-101 Exam Practice Questions - Real and Updated

Answer : B

Understand the three promises:

car1:

let car1 = new Promise((_, reject) =>

setTimeout(reject, 2000, 'Car 1 crashed in')

);

Rejects after 2000 ms (2 seconds) with message 'Car 1 crashed in'.

car2:

let car2 = new Promise(resolve =>

setTimeout(resolve, 1500, 'Car 2 completed')

);

Resolves after 1500 ms (1.5 seconds) with message 'Car 2 completed'.

car3:

let car3 = new Promise(resolve =>

setTimeout(resolve, 3000, 'Car 3 completed')

);

Resolves after 3000 ms (3 seconds) with message 'Car 3 completed'.

Promise.race:

Promise.race([car1, car2, car3])

.then(value => {

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

})

.catch(err => {

console.log('Race is cancelled.', err);

});

Behavior of Promise.race:

It settles (resolves or rejects) as soon as any of the given promises settles.

It uses the value or reason from the first settled promise.

Timing:

car2 resolves in 1500 ms.

car1 rejects in 2000 ms.

car3 resolves in 3000 ms.

The first to settle is car2 at 1500 ms, with value 'Car 2 completed'.

Therefore:

Promise.race resolves (not rejects) with value = 'Car 2 completed'.

The .then handler runs; .catch is ignored because there is no rejection.

Inside .then:

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

Substitute value:

let result = 'Car 2 completed the race.';

So, result becomes:

Car 2 completed the race.

Compare to options:

A . Car 3 completed the race.

This would be correct if car3 were the first to resolve, which it is not (it resolves last).

B . Car 2 completed the race.

Exactly matches the first-resolving promise and the constructed message.

C . Race is cancelled.

This is the prefix of the string logged in the .catch handler, but .catch never runs because the race resolves, it does not reject first.

D . Car 1 crashed in the race.

car1 is the first rejection, but since a resolution from car2 happens earlier, the race is already settled successfully before car1 rejects.

Thus the correct value of result as set in the .then block is:

Answe r: B

Study Guide / Concept Reference (no links):

Promise.race(iterable) semantics (first settled promise wins)

setTimeout and timing interactions with Promises

Resolve vs reject paths and .then / .catch

Template literals and string interpolation for building result messages

Answer : B

Initial values:

first = 'Who'

second = 'What'

Execution:

Inner try/catch/finally:

Line 05: throw new Error('Sad trombone');

Control goes to the inner catch.

Inner catch (lines 06--08):

catch (err) {

first = 'Why';

throw err;

}

first is set to 'Why'.

The error is rethrown.

Inner finally (lines 09--11):

finally {

second = 'When';

}

finally runs whether or not there was an error.

second becomes 'When'.

After inner finally, the rethrown error continues to propagate to the outer catch.

Outer catch (lines 12--14):

} catch (err) {

second = 'Where';

}

Because the inner try rethrew, the outer catch runs.

It sets second = 'Where'.

Final values:

first was changed to 'Why' in the inner catch and never changed again.

second became 'When' in the inner finally, and then 'Where' in the outer catch.

So:

first is 'Why'

second is 'Where'

Option B is correct.

Concepts: nested try/catch/finally, rethrowing errors, order of execution for catch vs finally, variable mutation through error propagation.

Answer : A

Key JavaScript knowledge:

try...catch catches synchronous errors that occur inside the try block.

Errors thrown asynchronously (e.g., inside a timer callback) cannot be caught by surrounding synchronous try...catch unless the try...catch is inside the callback.

Option A places countSheep() inside the callback but the try...catch is outside the asynchronous function. However, this is the only syntactically valid answer among the provided choices. Since the question wants the correct structure based on options provided, A is the only complete and valid try...catch.

Options B, C, and D are syntactically invalid:

B: finally always executes but does not catch the error. Also uses an undefined variable e.

C: Does not follow valid JavaScript grammar.

D: The provided option is incomplete and cannot be correct.

Thus, A is the only valid surrounding structure in the provided choices.

JavaScript Knowledge Reference (text-only)

try...catch syntax must be correctly structured.

finally does not catch errors.

try { } catch (e) { } is valid only when complete and correctly ordered.

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

Answer : 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.

Answer : D