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| Section | Weight | Objectives |
|---|---|---|
| Variables, Types, and Collections | 23% | - JSON parsing and manipulation - Variable declaration and scope - Strings, numbers, dates, arrays and methods - Data types, type coercion, truthy/falsy values |
| Asynchronous Programming | 13% | - Event loop and execution flow - Callbacks, promises, async/await |
| Testing | 7% | - Unit test structure and effectiveness - Test coverage and improvement |
| Objects, Functions, and Classes | 25% | - ES6 classes, inheritance, modules, decorators - Function types, scope, closures, arrow functions - Object creation, properties, prototypes |
| Debugging and Error Handling | 7% | - Error types and handling strategies - Console usage, breakpoints and debugging techniques |
| Browser and Events | 17% | - DOM selection and manipulation - Browser APIs and developer tools - Event handling, propagation, listeners |
| Server Side JavaScript | 8% | - Package management and CLI tools - Node.js fundamentals and core modules |
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NEW QUESTION # 39
JavaScript:
01 function Tiger() {
02 this.type = 'Cat';
03 this.size = 'large';
04 }
05
06 let tony = new Tiger();
07 tony.roar = () => {
08 console.log('They\'re great!');
09 };
10
11 function Lion() {
12 this.type = 'Cat';
13 this.size = 'large';
14 }
15
16 let leo = new Lion();
17 // Insert code here
18 leo.roar();
Which two statements could be inserted at line 17 to enable line 18?
Answer: B,C
Explanation:
________________________________________
Comprehensive and Detailed Explanation From Exact Extract JavaScript Knowledge There are two valid ways to ensure leo.roar() exists:
Directly assign a roar function to leo (Option A).
Assigning a property to an instance object creates a new method on that instance.
leo.roar = () => { console.log('They\'re pretty good!'); };
After this, calling leo.roar() is valid.
Copy tony's properties into leo using Object.assign (Option B).
Object.assign(target, source) copies enumerable own properties from the source object into the target object.
Since tony.roar exists, executing:
Object.assign(leo, tony);
copies roar into leo, making leo.roar() valid.
Why the other answers are incorrect:
Option C:
Object.assign(leo, Tiger) copies properties from the function object Tiger, not from Tiger.prototype and not from a Tiger instance. Tiger (the function) has no roar property, so nothing useful is copied.
Option D:
leo.prototype is undefined because leo is an instance, not a constructor function. Only constructor functions have a .prototype property. This line would cause an error.
________________________________________
JavaScript Knowledge Reference (text-only)
Instances have their own properties and do not contain a .prototype property.
Object.assign(target, source) copies own enumerable properties of the source object.
Assigning a function as a property of an object creates a callable method.
NEW QUESTION # 40
Refer to the code below (corrected to use a template literal on line 08):
01 let car1 = new Promise((_, reject) =>
02 setTimeout(reject, 2000, "Car 1 crashed in")
03 );
04 let car2 = new Promise(resolve =>
05 setTimeout(resolve, 1500, "Car 2 completed")
06 );
07 let car3 = new Promise(resolve =>
08 setTimeout(resolve, 3000, "Car 3 completed")
09 );
10
11 Promise.race([car1, car2, car3])
12 .then(value => {
13 let result = `${value} the race.`;
14 })
15 .catch(err => {
16 console.log("Race is cancelled.", err);
17 });
What is the value of result when Promise.race executes?
Answer: C
Explanation:
Comprehensive and Detailed Explanation From Exact Extract JavaScript knowledge:
Understand the three promises:
car1:
let car1 = new Promise((_, reject) =>
setTimeout(reject, 2000, "Car 1 crashed in")
);
Rejects after 2000 ms (2 seconds) with message "Car 1 crashed in".
car2:
let car2 = new Promise(resolve =>
setTimeout(resolve, 1500, "Car 2 completed")
);
Resolves after 1500 ms (1.5 seconds) with message "Car 2 completed".
car3:
let car3 = new Promise(resolve =>
setTimeout(resolve, 3000, "Car 3 completed")
);
Resolves after 3000 ms (3 seconds) with message "Car 3 completed".
Promise.race:
Promise.race([car1, car2, car3])
.then(value => {
let result = `${value} the race.`;
})
.catch(err => {
console.log("Race is cancelled.", err);
});
Behavior of Promise.race:
It settles (resolves or rejects) as soon as any of the given promises settles.
It uses the value or reason from the first settled promise.
Timing:
car2 resolves in 1500 ms.
car1 rejects in 2000 ms.
car3 resolves in 3000 ms.
The first to settle is car2 at 1500 ms, with value "Car 2 completed".
Therefore:
Promise.race resolves (not rejects) with value = "Car 2 completed".
The .then handler runs; .catch is ignored because there is no rejection.
Inside .then:
let result = `${value} the race.`;
Substitute value:
let result = "Car 2 completed the race.";
So, result becomes:
Car 2 completed the race.
Compare to options:
A . Car 3 completed the race.
This would be correct if car3 were the first to resolve, which it is not (it resolves last).
B . Car 2 completed the race.
Exactly matches the first-resolving promise and the constructed message.
C . Race is cancelled.
This is the prefix of the string logged in the .catch handler, but .catch never runs because the race resolves, it does not reject first.
D . Car 1 crashed in the race.
car1 is the first rejection, but since a resolution from car2 happens earlier, the race is already settled successfully before car1 rejects.
Thus the correct value of result as set in the .then block is:
Answe r: B
Study Guide / Concept Reference (no links):
Promise.race(iterable) semantics (first settled promise wins)
setTimeout and timing interactions with Promises
Resolve vs reject paths and .then / .catch
Template literals and string interpolation for building result messages
NEW QUESTION # 41
At Universal Containers, every team has its own way of copying JavaScript objects. The code Snippet shows an implementation from one team:
Function Person() {
this.firstName = "John";
this.lastName = 'Doe';
This.name =() => (
console.log('Hello $(this.firstName) $(this.firstName)');
)}
Const john = new Person ();
Const dan =JSON.parse(JSON.stringify(john));
dan.firstName ='Dan';
dan.name();
What is the Output of the code execution?
Answer: C
NEW QUESTION # 42
Given:
const str = 'Salesforce';
Which two statements result in 'Sales'?
Answer: B,C
Explanation:
str = 'Salesforce'
Index positions:
S(0) a(1) l(2) e(3) s(4) f(5) o(6) r(7) c(8) e(9)
substring(start, end)
Start index inclusive, end index exclusive.
str.substring(0, 5) → characters at indices 0-4 → "Sales"
str.substring(1, 5) → indices 1-4 → "ales"
substr(start, length)
Start index, then number of characters.
str.substr(0, 5) → 5 characters starting at index 0 → "Sales"
str.substr(1, 5) → 5 characters from index 1 → "alesf"
So the expressions that return "Sales" are A and C.
NEW QUESTION # 43
Refer to the HTML below:
<div id="main">
<ul>
<li>Leo</li>
<li>Tony</li>
<li>Tiger</li>
</ul>
</div>
Which JavaScript statement results in changing "Leo" to "The Lion"?
Answer: C
Explanation:
Comprehensive and Detailed Explanation From Exact Extract JavaScript Knowledge:
We want to select the first <li> under #main and change its content.
document.querySelector(selector) returns the first element matching the CSS selector.
In the DOM, the <li> elements under <ul> are children in order:
1st child: "Leo"
2nd child: "Tony"
3rd child: "Tiger"
li:nth-child(1) is the CSS pseudo-class that selects the first <li> inside its parent.
So:
document.querySelector('#main li:nth-child(1)').innerHTML = 'The Lion'; selects the first <li> ("Leo") inside #main and sets its innerHTML to "The Lion".
Why others are incorrect:
A . #main #Leo
There is no element with id "Leo". id is not set on the <li>, so the selector matches nothing.
B . li:second-child
There is no :second-child pseudo-class. The valid pseudo-class is :nth-child(2); and that would select "Tony", not "Leo".
C . '#main li,Leo'
This selector means "all #main li and all elements named <Leo>".
There is no <Leo> tag, and querySelectorAll returns a NodeList, which does not have a single innerHTML property.
Therefore, D is the correct statement.
Study Guide Concepts:
document.querySelector vs querySelectorAll
CSS selectors: nth-child()
DOM element innerHTML property
________________________________________
NEW QUESTION # 44
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