Explanation:

This question tests the understanding of variable scope, specifically the concept of implied globals and the difference between var, let, const, and undeclared variables.

Let's break down the code:
Line 01: setCurrentUrl(); - This calls the function setCurrentUrl.
Line 02: console.log('The current URL is: ' + url); - This attempts to log the value of a variable named url.
Line 03-05: The function setCurrentUrl is defined.
function setCurrentUrl() {
url = window.location.href;
}

The key is what happens inside the function on Line 04: url = window.location.href;
The variable url is not declared with var, let, or const inside the function.
In non-strict mode (which is likely the default context here), assigning a value to an undeclared variable implicitly creates a global variable.
Therefore, when setCurrentUrl() is executed on Line 01, it creates a global variable named url and assigns it the value of window.location.href.

Now, let's evaluate the options:
A. The url variable has local scope and line 02 throws an error. This is incorrect. Because the variable was not declared with var, let, or const inside the function, it does not have local scope. It becomes a global.
B. The url variable has global scope and line 02 executes correctly. This is correct. As explained, the assignment inside the function without a declaration creates a global variable. By the time Line 02 executes, the global variable url exists and holds a value, so the console.log statement works without throwing an error.
C. The url variable has global scope and line 02 throws an error. This is incorrect. While the variable does have global scope, Line 02 will not throw an error because the variable exists in the global scope when the line is executed.
D. The url variable has local scope and line 02 executes correctly. This is incorrect. The variable does not have local scope (it's global), and if it did have local scope (e.g., if it was declared with let url = ...), then Line 02 would indeed throw a ReferenceError because it would be trying to access a variable from a scope where it is not defined.

Reference:
MDN Web Docs on undeclared variables:
The concept of "implied globals" is a classic behavior of JavaScript's non-strict mode.

Conclusion:
The code creates a global variable, allowing the console.log statement to access it and execute successfully.

Explanation:

🧠 Problem Breakdown
Here’s the broken code (cleaned up for clarity):
const sumFunction = arr => {
return arr.reduce((result, current) => {
result += current;
// Missing return here!
}, 10);
};

The issue:
The callback inside reduce() is not returning the updated result.
In arrow functions with {}, you must explicitly return a value.
Without a return, reduce() passes undefined as the accumulator in the next iteration.

D. Replace line 05 with return result;
This fixes the function by ensuring the callback returns the updated accumulator:
const sumFunction = arr => {
return arr.reduce((result, current) => {
result += current;
return result;
}, 10);
};

❌ Why the other options fail:
A. Replace with map()❌
map() returns a new array, not a sum. Wrong method.
B. Use result = result + current; ❌
Still missing return result; — syntax is fine, logic still broken.
C. Add if(arr.length == 0) return 0; ❌
Defensive coding, but doesn’t fix the missing return inside reduce().
D. Add return result; ✅
Corrects the missing return inside the reduce() callback.

🔁 Bonus Tip:
You can simplify the function using an implicit return:
const sumFunction = arr => arr.reduce((result, current) => result + current, 10);

Explanation:

🔎 Key facts
In Node.js, objects that emit events (like http.Server) are instances of EventEmitter.
To listen for errors, you must register an error event listener:
server.on('error', (error) => {
console.error('ERROR', error);
});

catch only works with synchronous errors in a try...catch block. Asynchronous events (like server boot errors) must be handled with .on('error', …).

❌ Wrong options
A. server.catch(...)
No .catch() method on EventEmitter objects. That’s for Promises. ❌
B. server.error(...)
Not a valid method. Error events must be attached with .on('error', …). ❌
D. try { server.start(); } catch(error) {...}
Won’t catch async startup issues — only synchronous code inside start() itself. ❌

✅ Correct option
C. server.on('error', (error) => { console.log('ERROR', error); });
This is the correct way to handle startup or runtime errors emitted by a Node.js server.

📚 Reference:
Node.js – EventEmitter error event
Node.js HTTP Server error handling

Explanation:

Code Analysis
let x = ('15' + 10) * 2;
'15' + 10: The + operator concatenates the string '15' with the number 10 (coerced to '10'), resulting in the string '1510'.
'1510' * 2: The * operator coerces the string '1510' to the number 1510, then multiplies by 2, yielding 3020.
x is assigned 3020 (a number).
The question asks for a, but the code defines x. Assuming a typo (common in exam questions), the value of x is 3020. No information is provided about a.

Options
A. 3020: Correct, matches the result.
B. 1520: Incorrect, would require numeric addition (15 + 10), not concatenation.
C. 50: Incorrect, assumes numeric addition 15 + 10 = 25, then 25 * 2.
D. 35: Incorrect, misinterprets the operation (e.g., 15 + 10 + 10).

Explanation Notes
JavaScript’s + operator performs string concatenation when one operand is a string.
The * operator coerces a numeric string to a number for multiplication.
The question likely meant x instead of a. If a is a separate variable, additional context is needed.

References:
MDN: Addition (+)
MDN: Type Coercion
Salesforce JavaScript Developer I exams test type coercion and operator behavior.

Explanation:

This question tests the knowledge of JavaScript methods used to control the mutability of objects. The requirement is to make an object's properties immutable and to prevent properties from being added or modified. This is the exact functionality provided by Object.freeze().

Let's break down what Object.freeze() does:
Makes existing properties non-writable: You cannot change their values.
Makes existing properties non-configurable: You cannot delete them or change their attributes (e.g., make them writable again).
Prevents new properties from being added: The object becomes sealed against any extensions.
After calling Object.freeze(obj), any attempt to add, modify, or delete properties will fail silently in non-strict mode or throw a TypeError in strict mode.

Example:
const myObject = {
prop1: 42,
prop2: 'Hello World'
};

Object.freeze(myObject);

myObject.prop1 = 100; // This assignment will fail silently (or throw an error in strict mode) console.log(myObject.prop1); // Output: 42 (unchanged)
myObject.prop3 = 'New'; // Fails, cannot add new properties
delete myObject.prop2; // Fails, cannot delete properties

Now, let's evaluate why the other options are incorrect:
A. Object.const():
This method does not exist in JavaScript. The const keyword is used for declaring block-scoped variables, but it does not make the object itself immutable. A const object can still have its properties modified (e.g., const obj = {}; obj.a = 1; is allowed).
B. Object.eval():
This method does not exist for the purpose of immutability. The global eval() function is used to evaluate JavaScript code represented as a string, and its use is generally discouraged due to security and performance implications. It has nothing to do with controlling object properties.
C. Object.lock():
This method does not exist in standard JavaScript. It might be a distractor based on similar concepts in other programming languages.

Reference:
MDN Web Docs on Object.freeze():

Conclusion:
To fulfill the business requirement of making an object completely immutable—preventing any additions, modifications, or deletions of its properties—the correct method to use is Object.freeze().

Explanation:

This code snippet uses event delegation, a powerful technique where a single event listener is placed on a parent element to manage events for all its child elements. The event listener is on the document.body, and it listens for a click event anywhere on the page.

The event.target property refers to the specific element that was clicked.
The nodeName property of an element returns the name of the node, which for HTML elements is the tag name in uppercase. For a button, this would be 'BUTTON'.

Therefore, by checking if event.target.nodeName is equal to 'BUTTON', the developer can accurately determine if the clicked element was a button.

Why Other Options Are Incorrect
A. Event.clicked:
clicked is not a standard property of the Event object. This would result in an error or an undefined value.
B. e.nodeTarget == this:
e.nodeTarget is not a standard property; the correct property is event.target.
In an arrow function, this refers to the parent scope, which in this case is the document.body. This comparison would only be true if the document.body itself was clicked, not a child button.
D. button.addEventListener('click'):
This is a method call, not a conditional statement. It would attempt to add an event listener inside the if condition, which is syntactically and logically incorrect.

Explanation:

🔍 Original Expression:
let x = ('1' + 2) == (6 * 2);
Breakdown:
'1' + 2 → '12' (string concatenation)
6 * 2 → 12 (number)
'12' == 12 → true (because == does type coercion)

❓Goal:
We want to modify the expression so it evaluates to false.

✅ Correct Answer:
A. let x = ('1' + ' 2') == (6 * 2);

Why?
'1' + ' 2' → '1 2' (note the space!)
6 * 2 → 12
'1 2' == 12 → false Because '1 2' is not coercible to the number 12.

❌ Why the other options fail:
B. '1' + 2 == 12
✅ true Same as original — still evaluates to true.
C. (1 + 2) == ('6' / 2)
✅ true 3 == 3 — both sides are numbers.
D. (1 + 2) == (6 / 2)
✅ true 3 == 3 again — still true.

🧠 Key Concepts:
+ with a string → triggers string concatenation
== → performs type coercion
To force false, you need non-equivalent values after coercion

Explanation:

🔎 Key facts:
Node.js has a built-in https module for creating secure (SSL/TLS) web servers.
The http module is for plain, non-secure servers.
The tls module handles lower-level TLS/SSL sockets, but it’s not used directly to serve HTTPS web traffic.
There is no built-in secure-server module — that’s a fake distractor.

Check options:
A. const https = require('https'); ✅
Correct! This loads Node’s core https module, used to create secure HTTPS servers.
B. const server = require('secure-server'); ❌
Not a real Node.js core module.
C. const tls = require('tls'); ❌
This provides raw TLS socket support. Too low-level for setting up a web server.
D. const http = require('http'); ❌
This creates insecure HTTP servers, not HTTPS.
✅ Correct Answer: A. const https = require('https');

📚 Reference:
Node.js Docs – https module
Node.js Docs – http module

Explanation:

Replacing the database.query dependency with a stand-in object that returns a fixed array without inspecting its internal behavior or verifying invocation counts is characteristic of stubbing and black-box testing. Stubbing provides a lightweight test double that returns predetermined data. Black-box testing focuses on inputs and outputs, ignoring the internal implementation and call frequency. White-box testing would require awareness of internal logic and verifying interactions, which is not needed here. Substitution is not a formal testing term in mainstream methodologies. Therefore, the appropriate approaches are stubbing to replace dependencies and black-box testing to validate behavior purely by the returned data.

Explanation:

With the updated sum3 that sums all elements, calling sum3([1,2,3]) still returns 6, so the first console.assert(res === 6) passes. However, sum3([1,2,3,4]) now returns 10, not 6, so the second assertion fails. Thus, line 02 succeeds (A), and line 05 fails (D). This highlights the importance of writing tests that capture intended behavior changes: when functionality broadens from summing only the first three items to summing the entire array, existing tests may no longer validate correct behavior for all inputs.

Explanation:

Because runParallel() is an async function, it returns a Promise. You consume its result via the Promise API’s .then(...) handler. Options C and D correctly call runParallel() and attach a .then callback to process its resolved value. Option A incorrectly prefixes with Async, which isn’t valid syntax for invocation. Option B uses .done(...), a non-standard Promise method (found in some libraries but not native JavaScript). Always use .then(...) or await to handle async function results in modern JavaScript.

Explanation:

You first double each grade using Array.prototype.map(), producing [14,16,10,16,18]. Then you filter scores above 15 with Array.prototype.filter(), yielding [16,16,18]. This chaining ensures the mapping happens before filtering. Option A reverses the order (filter then map), B and D use non-standard methods (mapBy/filterBy), which don’t exist in vanilla JavaScript. Option C correctly leverages built-in map and filter methods in the proper sequence to meet the teacher’s requirements.