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NEW QUESTION # 38
Refer to the code below:
Let str = 'javascript';
Str[0] = 'J';
Str[4] = 'S';
After changing the string indexvalues, the value of str is 'javascript'. What is the reason for this value:
Answer: C
NEW QUESTION # 39
Refer to the code:
01 const event = new CustomEvent(
02 // Missing code
03 );
04 obj.dispatchEvent(event);
A developer needs to dispatch a custom event called update to send information about recordId.
Which two options can be inserted at line 02?
Answer: B,C
Explanation:
________________________________________
Comprehensive and Detailed Explanation From Exact Extract JavaScript Knowledge The correct constructor signature for CustomEvent is:
new CustomEvent(eventName, optionsObject)
Where:
eventName is a string.
optionsObject may include:
detail → used to pass custom data
bubbles
cancelable, etc.
Example:
new CustomEvent('update', {
detail: { recordId: '123abc' }
});
Now evaluate each option:
________________________________________
Option A
{ type: 'update', recordId: '123abc' }
Incorrect: The constructor requires (eventName, options), not a single object. type is not used this way.
________________________________________
Option B
'update', { detail: { recordId: '123abc' } }
Correct format. detail is the proper place for custom event data.
________________________________________
Option C
'update', '123abc'
Incorrect: The second argument must be an object (options), not a string.
________________________________________
Option D
'update', { recordId: '123abc' }
Acceptable because any extra properties on the options object are still allowed, even though best practice is to use detail.
This still creates a valid CustomEvent, and the event will dispatch successfully.
Thus the two correct answers are B and D.
________________________________________
JavaScript Knowledge Reference (text-only)
new CustomEvent(name, options) is the required syntax.
The detail property of the options object is the standard location for custom data.
The second argument must be an object; other types are invalid.
NEW QUESTION # 40
Given the requirement to refactor the code above to JavaScript class format, which class definition is correct?
Answer: D
NEW QUESTION # 41
Refer to the code below (corrected to use a template literal on line 08):
01 let car1 = new Promise((_, reject) =>
02 setTimeout(reject, 2000, "Car 1 crashed in")
03 );
04 let car2 = new Promise(resolve =>
05 setTimeout(resolve, 1500, "Car 2 completed")
06 );
07 let car3 = new Promise(resolve =>
08 setTimeout(resolve, 3000, "Car 3 completed")
09 );
10
11 Promise.race([car1, car2, car3])
12 .then(value => {
13 let result = `${value} the race.`;
14 })
15 .catch(err => {
16 console.log("Race is cancelled.", err);
17 });
What is the value of result when Promise.race executes?
Answer: B
Explanation:
Understand the three promises:
car1:
let car1 = new Promise((_, reject) =>
setTimeout(reject, 2000, "Car 1 crashed in")
);
Rejects after 2000 ms (2 seconds) with message "Car 1 crashed in".
car2:
let car2 = new Promise(resolve =>
setTimeout(resolve, 1500, "Car 2 completed")
);
Resolves after 1500 ms (1.5 seconds) with message "Car 2 completed".
car3:
let car3 = new Promise(resolve =>
setTimeout(resolve, 3000, "Car 3 completed")
);
Resolves after 3000 ms (3 seconds) with message "Car 3 completed".
Promise.race:
Promise.race([car1, car2, car3])
.then(value => {
let result = `${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
NEW QUESTION # 42
A developer has a fizzbuzz function that, when passed in a number, returns the following:
'fizz' if the number is divisible by 3.
'buzz' if the number is divisible by 5.
'fizzbuzz' if the number is divisible by both 3 and 5.
Empty string '' if the number is divisible by neither 3 nor 5.
Which two test cases properly test scenarios for the fizzbuzz function?
Answer: A,C
Explanation:
Comprehensive and Detailed Explanation From Exact Extract JavaScript knowledge:
First, recall the fizzbuzz rules:
If n divisible by 3 and not by 5 → return 'fizz'.
If n divisible by 5 and not by 3 → return 'buzz'.
If n divisible by both 3 and 5 → return 'fizzbuzz'.
Otherwise → return '' (empty string).
Evaluate each test:
Option A:
let res = fizzbuzz(true);
console.assert(res === '');
In JavaScript, when using arithmetic operations with true, it is coerced to the number 1. A typical implementation of fizzbuzz would treat the argument as a number and compute:
true % 3 → 1 % 3 → 1
true % 5 → 1 % 5 → 1
So true is effectively treated as 1, which is divisible by neither 3 nor 5. The function should return ''. The assertion res === '' will pass.
This test covers the scenario "neither divisible by 3 nor 5".
Option B:
let res = fizzbuzz(3);
console.assert(res === '');
3 is divisible by 3 but not by 5.
According to fizzbuzz rules, fizzbuzz(3) should return 'fizz'.
This test expects '', so it is incorrect; the assertion would fail in a correct implementation.
Option C:
let res = fizzbuzz(5);
console.assert(res === 'fizz');
5 is divisible by 5 but not by 3.
According to fizzbuzz rules, fizzbuzz(5) should return 'buzz'.
This test expects 'fizz', so it is incorrect.
Option D:
let res = fizzbuzz(15);
console.assert(res === 'fizzbuzz');
15 is divisible by both 3 and 5.
According to fizzbuzz rules, fizzbuzz(15) should return 'fizzbuzz'.
This assertion correctly matches the expected result, so it is a proper test case.
Thus, the two test cases that correctly test valid fizzbuzz behavior are:
Study Guide / Concept Reference (no links):
Modulo operator (%) for divisibility checks
Truthy/number coercion of boolean true in arithmetic (Number(true) === 1) Designing unit tests with console.assert Typical fizzbuzz logic structure and expected outputs
________________________________________
NEW QUESTION # 43
......
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