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NEW QUESTION # 62
A developer wants to catch any error that countSheep() may throw and pass it to handleError().
Which implementation is correct?
Answer: A
Explanation:
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.
NEW QUESTION # 63
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: A,D
Explanation:
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 # 64
developer publishes a new version of a package with new features that do not break backward compatibility. The previous version number was 1.1.3.
Following semantic versioning format, what should the new package version number be?
Answer: D
NEW QUESTION # 65
Refer to the following code block (with corrected template literals using backticks):
01 class Animal {
02 constructor(name) {
03 this.name = name;
04 }
05
06 makeSound() {
07 console.log(`${this.name} is making a sound.`);
08 }
09 }
10
11 class Dog extends Animal {
12 constructor(name) {
13 super(name);
14 this.name = name;
15 }
16 makeSound() {
17 console.log(`${this.name} is barking.`);
18 }
19 }
20
21 let myDog = new Dog('Puppy');
22 myDog.makeSound();
What is the console output?
Answer: B
Explanation:
Animal class:
Has a constructor that sets this.name.
Has a makeSound method that logs a message using this.name.
Dog class:
Extends Animal.
Its constructor calls super(name) to run the parent constructor, which sets this.name.
It overrides makeSound() to log:
console.log(`${this.name} is barking.`);
Instantiation:
let myDog = new Dog('Puppy');
myDog.makeSound();
new Dog('Puppy'):
Calls Dog constructor with name = 'Puppy'.
Inside, super(name) sets this.name = 'Puppy' in the Animal constructor.
Then this.name = name; in the Dog constructor keeps it as 'Puppy'.
myDog.makeSound():
Calls the overridden makeSound() in Dog.
Logs: "Puppy is barking."
No reference errors, no undefined; the output is:
Puppy is barking.
Study Guide Concepts:
ES6 classes and inheritance (extends)
super() in subclass constructors
Method overriding in subclasses
Template literals: `${this.name} ...`
NEW QUESTION # 66
Refer to the following array:
let arr = [1, 2, 3, 4, 5];
Which two lines of code result in a second array, arr2, created such that arr2 is a reference to arr?
Answer: A,B
Explanation:
The correct answers are C and D.
Arrays in JavaScript are objects. When an array variable is assigned directly to another variable, both variables point to the same array in memory.
Option C is correct:
let arr2 = arr;
This does not create a new array. It creates another reference to the same array.
Example:
arr2.push(6);
console.log(arr);
Output:
[1, 2, 3, 4, 5, 6]
Changing arr2 also affects arr because both variables reference the same array.
Option D is also correct:
let arr2 = arr.sort();
The sort() method sorts the array in place and returns the same array reference. Therefore, arr2 refers to the same array object as arr.
The incorrect options create copies:
let arr2 = arr.slice(0, 5);
creates a shallow copy.
let arr2 = Array.from(arr);
also creates a new shallow copy.
So the two lines that make arr2 reference the original arr are C and D.
NEW QUESTION # 67
......
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