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NEW QUESTION # 88
A developer is creating a simple webpage with a button. When a user clicks this button for the first time, a message is displayed.
The developer wrote the JavaScript code below, but something is missing. The message gets displayed every time a user clicks the button, instead of just the first time.
01 function listen(event) {
02
03 alert('Hey! I am John Doe');
04
05 }
06 button.addEventListener('click', listen);
Which two code lines make this code work as required?
Answer: A,B
Explanation:
Requirement:
The message should be displayed only on the first click of the button.
Original behavior:
The handler listen is attached with button.addEventListener('click', listen);.
That means listen is called on every click until the listener is removed or configured otherwise.
Two correct ways to ensure the listener only fires once:
Use the once option in addEventListener
Remove the event listener after the first run inside the handler
Option C:
On line 06, add an option called once to button.addEventListener().
This means modifying line 06 to:
button.addEventListener('click', listen, { once: true });
The once: true option tells the browser:
Call the listen function at most once.
After it is called the first time, automatically remove the listener.
So:
First click: alert shows, listener is removed automatically.
Subsequent clicks: no further calls to listen, no alerts.
This satisfies the requirement.
Option D:
On line 04, use button.removeEventListener('click', listen);
This means updating the handler:
function listen(event) {
alert('Hey! I am John Doe');
button.removeEventListener('click', listen);
}
Now:
On the first click, listen is executed:
It shows the alert.
It removes itself from the button's click listeners.
On subsequent clicks, listen is no longer registered, so nothing happens.
This also satisfies the requirement.
Why A and B are incorrect:
Option A:
On line 04, use event.stopPropagation();
event.stopPropagation() stops the event from bubbling up the DOM tree.
It does not prevent the current listener from being called again in the future.
The click handler will still run on every click; it just prevents other listeners higher in the DOM from receiving the event.
Option B:
On line 02, use event.first to test if it is the first execution.
There is no built-in event.first property in standard DOM events.
This property does not exist and will be undefined.
You would need your own external flag (let hasRun = false;) to track first execution, but that is not what B describes.
Therefore, the two correct modifications are:
Answe r: C, D
Study Guide / Concept Reference (no links):
addEventListener options object: { once: true }
removeEventListener to manually deregister event handlers
Event propagation (event.stopPropagation) vs handler lifecycle
DOM event model and listener registration
NEW QUESTION # 89
A 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 formats, what should the new package version number be?
Answer: B
Explanation:
The correct answer is D.
Semantic versioning usually follows this format:
MAJOR.MINOR.PATCH
For the version:
1.1.3
The parts are:
1 = MAJOR
1 = MINOR
3 = PATCH
A package version should be updated based on the type of change:
MAJOR version changes when there are breaking changes.
MINOR version changes when new features are added in a backward-compatible way.
PATCH version changes when backward-compatible bug fixes are added.
The question says the developer added new features that do not break backward compatibility. That means the minor version should increase.
Starting version:
1.1.3
Increase the minor version from 1 to 2, and reset the patch version to 0:
1.2.0
Why the other options are incorrect:
A . 1.2.3 is incorrect because when the minor version increases, the patch version should reset to 0.
B . 1.1.4 is incorrect because that would represent a patch update, usually for bug fixes, not new features.
C . 2.0.0 is incorrect because that would represent a major version update, usually for breaking changes.
D . 1.2.0 is correct because it represents a backward-compatible feature release.
Therefore, the verified answe r is D.
NEW QUESTION # 90
Refer to the following array:
Let arr = [ 1,2, 3, 4, 5];
Which three options result in x evaluating as [3, 4, 5] ?
Choose 3 answers.
Answer: C,D,E
NEW QUESTION # 91
A developer creates a new web server that uses Node.js. It imports a server library that uses events and callbacks for handling server functionality. The server library is imported with require and is made available to the code by a variable named server. The developer wants to log any issues that the server has while booting up.
Which code logs an error at boot time with an event?
Answer: D
Explanation:
Event-driven Node-style APIs expose events via .on(eventName, handler).
To listen for error events:
server.on('error', (error) => {
console.log('ERROR', error);
});
A and B assume methods .error or .catch that don't exist on typical event emitters.
C only catches synchronous errors from server.start(), not async event-based errors.
________________________________________
NEW QUESTION # 92
Refer to the code:
const pi = 3.1415926;
What is the data type of pi?
Answer: D
Explanation:
________________________________________
Comprehensive and Detailed Explanation From Exact Extract JavaScript Knowledge JavaScript has one numeric data type for all real numbers, whether integers or decimals.
This type is simply called:
Number
It follows the IEEE 754 double-precision floating-point standard internally, but JavaScript does not expose separate types like float, double, or decimal.
Therefore:
It is not Float → JavaScript does not have float primitives.
It is not Double → this refers to the underlying IEEE 754 representation, but JavaScript's type is still just "Number." It is not Decimal → JavaScript has no built-in decimal type.
The correct answer is Number.
________________________________________
JavaScript Knowledge Reference (text-only)
JavaScript has a single numeric type: Number.
All numbers-integers, fractions, floating point-use the Number type.
NEW QUESTION # 93
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