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| Section | Weight | Objectives |
|---|---|---|
| Asynchronous Programming | 13% | - Async/Await syntax - Asynchronous patterns for business requirements - Callbacks - Event loop and execution flow - Promises (creation, chaining, error handling) |
| Server Side JavaScript | 8% | - Package management (npm) - Server-side JavaScript implementations - CLI commands - Node.js fundamentals - Core Node.js modules |
| Objects, Functions, and Classes | 25% | - Object creation and manipulation - ES6 classes and inheritance - Variable scope and closures - Execution flow and context - Prototypal inheritance - Higher-order functions - Modules and decorators - Function declarations and expressions - Arrow functions |
| Browser and Events | 17% | - Browser-specific APIs - Event propagation (bubbling and capturing) - Interacting with forms and user input - DOM manipulation - Event handling and listeners - Browser Developer Tools usage |
| Variables, Types, and Collections | 23% | - Variable declarations and initialization - Truthy and falsy evaluations - Strings, numbers, and dates - Arrays and collections - JSON parsing and manipulation - Type coercion and conversion - Primitive and complex data types |
| Debugging and Error Handling | 7% | - Custom error types - Error handling techniques (try/catch/finally) - Breakpoints and code inspection - Console methods for debugging |
| Testing | 7% | - Writing and modifying unit tests - Test coverage and reliability - Unit testing concepts - Test effectiveness evaluation |
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NEW QUESTION # 62
Given the following code:
Let x =('15' + 10)*2;
What is the value of a?
Answer: A
NEW QUESTION # 63
At Universal Containers, every team has its own way of copying JavaScript objects. The code snippet shows an Implementation from one team:
What is the output of the code execution?
Answer: A
NEW QUESTION # 64
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: B,D
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:
The answer: C, D
Study Guide / Concept References (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 # 65
A developer wants to use a try...catch statement to catch any error that countSheep () may throw and pass it to a handleError () function.
What is the correct implementation of the try...catch?
A)
B)
C)
D)
Answer: B
NEW QUESTION # 66
Refer to the code below:
const car = {
price:100,
getPrice:function(){
return this.price;
}
};
const customCar = Object.create(car);
customCar.price = 70;
delete customCar.price;const result = customCar.getPrice();
What is the value of result after the code executes?
Answer: A
NEW QUESTION # 67
......
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