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>> Clearer JS-Dev-101 Explanation <<
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NEW QUESTION # 90
Given the following code:
What is the output of line 02?
Answer: D
NEW QUESTION # 91
Refer to the code below:
01 const addBy = ?
02 const addByEight = addBy(8);
03 const sum = addByEight(50);
Which two functions can replace line 01 and return 58 to sum?
Answer: B,D
Explanation:
}
Explanation:
Comprehensive and Detailed Explanation From Exact Extract JavaScript knowledge:
We want:
const addByEight = addBy(8);
const sum = addByEight(50);
And we need sum to be 58.
That means:
addBy(8) must return a function.
That returned function, when called with 50, must compute 8 + 50.
So addBy must be a higher-order function that returns another function capturing num1 and later using it with num2 (a closure).
Option A
const addBy = function(num1) {
return function(num2) {
return num1 + num2;
}
}
Step-by-step:
Call addBy(8):
num1 is 8.
The function returns an inner function: function(num2) { return num1 + num2; }.
So addByEight becomes this inner function, with num1 closed over as 8.
Then call addByEight(50):
num2 is 50.
The body computes num1 + num2, i.e., 8 + 50 = 58.
Therefore, with Option A in place:
const addByEight = addBy(8); // returns inner function
const sum = addByEight(50); // 58
So sum is 58. Option A is correct.
Option D (corrected)
const addBy = (num1) => {
return function(num2) {
return num1 + num2;
}
}
This is essentially the same logic expressed with an arrow function for the outer function:
Call addBy(8):
num1 is 8.
Returns the inner function function(num2) { return num1 + num2; }.
Call addByEight(50):
num2 is 50.
Computes num1 + num2 → 8 + 50 = 58.
So again:
const addByEight = addBy(8); // inner function with num1 = 8
const sum = addByEight(50); // 58
Option D is also correct.
Thus, A and D are the two functions that satisfy the requirement.
Why B and C are incorrect
Option B:
const addBy = function(num1) {
return num1 * num2;
}
This does not return a function; it returns a value.
addBy(8) returns 8 * num2, but num2 is not defined in this scope, which would cause a ReferenceError.
Also, addByEight would be a number (if num2 existed), not a function, so addByEight(50) would fail.
Option C:
const addBy = (num1) => num1 + num2;
Again, addBy returns a value, not a function.
addBy(8) returns 8 + num2, but num2 is not defined, so this is also invalid due to ReferenceError.
addByEight would be a number (or error), not a function.
Neither B nor C creates the required closure nor returns a function to be called later.
Reference / Study Guide concepts (no links):
Higher-order functions in JavaScript
Closures: inner functions capturing outer variables (num1)
Arrow functions vs function expressions
Returning functions from functions (function factories / currying)
Scope and ReferenceError when a variable is not defined
________________________________________
NEW QUESTION # 92
Given two expressions var1 and var2, what are two valid ways to return the concatenation of the two expressions and ensure it is data type string?
Answer: A,C
Explanation:
Comprehensive and Detailed Explanation From JavaScript Knowledge:
We want to guarantee that the result is of type string regardless of what var1 and var2 are (numbers, booleans, etc.).
Option A:
String(var1).concat(var2)
String(var1) converts var1 explicitly to a string.
.concat(var2) calls String.prototype.concat, which:
Converts var2 to string if needed.
Returns a new string that is the concatenation of the two.
Result is always a string.
So A is valid.
Option B:
String.concat(var1 + var2)
String.concat (as a static method) does not exist. concat is an instance method on string objects, not on the String constructor.
var1 + var2 might be a number (if both numeric) and used incorrectly here.
So B is invalid.
Option C:
var1 + var2
+ can mean:
String concatenation (if at least one operand is a string).
Numeric addition (if both operands are numbers).
If var1 and var2 are both numbers, var1 + var2 will be a number, not a string.
This does not ensure the result is always a string.
So C is not guaranteed to satisfy the requirement.
Option D:
var1.toString() + var2.toString()
var1.toString() converts var1 to a string (for most primitive/object types).
var2.toString() does the same.
Now both operands of + are strings, so the result is string concatenation.
Result is guaranteed to be a string.
So D is valid.
Therefore, the two valid ways are A and D.
Study Guide / Concept Reference (no links):
String() conversion vs .toString()
String.prototype.concat
+ operator overload: numeric addition vs string concatenation
Type coercion rules for primitives
________________________________________
NEW QUESTION # 93
Which three browser specific APIs are available for developers to persist data between page loads?
Answer: A,D,E
Explanation:
A pattern for creating a new scope, not a persistence mechanism.
Variables inside an IIFE are still lost when the page reloads.
Thus, the three persistent browser APIs are:
localStorage
indexedDB
cookies
Explanation:
Comprehensive and Detailed Explanation From Exact Extract JavaScript knowledge:
We want mechanisms that persist data between page loads (i.e., after refresh or navigation), in the browser.
A . localStorage
Part of the Web Storage API.
Data persists across page reloads and browser restarts (until explicitly cleared).
Scoped per origin (protocol + host + port).
This is a correct persistent storage API.
B . indexedDB
A low-level, client-side NoSQL database in the browser.
Stores large amounts of structured data and persists across reloads and sessions.
This is also a correct persistent API.
C . cookies
Small key/value pairs stored by the browser and often sent with HTTP requests.
Can have expiration dates and persist across page loads and sessions.
They are a traditional persistence mechanism in browsers.
So cookies also qualify.
D . global variables
Global JS variables exist only for the life of the current page context.
When the page is refreshed or navigated away, they are lost.
They do not persist between page loads.
NEW QUESTION # 94
A developer at Universal Containers is creating their new landing pagebased on HTML, CSS, and JavaScript. The website includes multiple external resources that are loaded when the page is opened.
To ensure that visitors have a good experience, a script named personalizeWebsiteContent needs to be executed when the webpage isloaded and there is no need to wait for the resources to be available.
Which statement should be used to call personalizeWebsiteContent based on the above business requirement?
Answer: D
NEW QUESTION # 95
......
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