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NEW QUESTION # 133
Refer to the code below:
01 let country = {
02 get capital() {
03 let city = Number("London");
04
05 return {
06 cityString: city.toString(),
07 }
08 }
09 }
Which value can a developer expect when referencing country.capital.cityString?
Answer: C
Explanation:
________________________________________
Comprehensive and Detailed Explanation From Exact Extract JavaScript Knowledge In the getter:
let city = Number("London");
The Number() constructor attempts to convert the string "London" into a numeric value.
"London" is not a valid numeric string.
When JavaScript attempts numeric conversion of a non-numeric string:
Number("London") โ NaN
Next line:
city.toString()
When city is NaN, calling .toString() yields:
NaN.toString() โ "NaN"
The getter returns:
{
cityString: "NaN"
}
The question asks:
Which value can a developer expect?
The multiple-choice options include NaN, but not "NaN".
Given the available choices, the intended correct answer is B (NaN) because the root cause is the Number("London") conversion returning NaN.
________________________________________
JavaScript Knowledge Reference (text-only)
Number(nonNumericString) returns NaN.
NaN.toString() produces "NaN".
Getters compute and return their values each time the property is accessed.
NEW QUESTION # 134
Which three browser specific APIs are available for developers to persist data between page loads ?
Choose 3 answers
Answer: A,B,D
NEW QUESTION # 135
Given the code:
01 function GameConsole(name) {
02 this.name = name;
03 }
04
05 GameConsole.prototype.load = function(gamename) {
06 console.log('${this.name} is loading a game: ${gamename}....');
07 }
08
09 function Console16bit(name) {
10 GameConsole.call(this, name);
11 }
12
13 Console16bit.prototype = Object.create(GameConsole.prototype);
14
15 // insert code here
16 console.log('${this.name} is loading a cartridge game: ${gamename}....');
17 }
18
19 const console16bit = new Console16bit('SNEGeneziz');
20 console16bit.load('Super Monic 3x Force');
What should a developer insert at line 15?
Answer: C
Explanation:
A subclass created by:
Console16bit.prototype = Object.create(GameConsole.prototype);
inherits all prototype methods from GameConsole, including load.
To override the inherited method, the correct syntax is to assign a new function to the method name on the prototype:
Console16bit.prototype.load = function(gamename) {
console.log(`${this.name} is loading a cartridge game: ${gamename}....`);
};
Why the other options are wrong:
A assigns something to the constructor function itself, not to the prototype method. Invalid.
B attempts to call a function in the left-hand side of an assignment; invalid syntax.
C also uses invalid syntax-prototype methods cannot be defined this way.
D is the correct definition of a prototype method override.
JavaScript Knowledge Reference (text-only)
Methods are overridden by assigning functions to Subclass.prototype.methodName.
Object.create() establishes prototype inheritance.
Constructor functions require prototype method attachment using assignment syntax.
NEW QUESTION # 136
A developer creates a class that represents a news story based on the requirements that a Story should have a body, author, and view count. The code is shown below:
01 class Story {
02 // Insert code here
03 this.body = body;
04 this.author = author;
05 this.viewCount = viewCount;
06 }
07 }
Which statement should be inserted in the placeholder on line 02 to allow for a variable to be set to a new instance of a Story with the three attributes correctly populated?
Answer: A
Explanation:
Comprehensive and Detailed Explanation From Exact Extract JavaScript knowledge:
In ES6 class syntax, the special method used to initialize a new instance is called constructor.
A class definition syntax:
class ClassName {
constructor(param1, param2) {
this.prop1 = param1;
this.prop2 = param2;
}
}
The constructor method:
Is called automatically when you create a new instance with new ClassName(...).
Receives the arguments passed in the new expression.
Assigns values to this to set instance properties.
Applying this to Story
We want to be able to write:
const article = new Story('Some body', 'Author Name', 100);
and have:
article.body === 'Some body'
article.author === 'Author Name'
article.viewCount === 100
To achieve this, the class must have:
class Story {
constructor(body, author, viewCount) {
this.body = body;
this.author = author;
this.viewCount = viewCount;
}
}
So the correct line 02 is:
constructor(body, author, viewCount) {
Why the other options are incorrect
A . constructor() {
This defines a constructor with no parameters.
The lines inside the constructor use body, author, and viewCount, which would be undefined unless they exist in an outer scope (they normally do not).
This would lead to the instance properties being set to undefined in normal usage.
B . super(body, author, viewCount) {
super(...) is used inside a constructor of a subclass to call the parent class constructor.
You cannot use super(...) { as a method definition; this is invalid syntax in a class body.
Additionally, Story as given is not shown extending any class, so super is inappropriate here.
C . function Story(body, author, viewCount) {
Inside a class definition, you do not use the function keyword to define methods.
function Story(...) here would be invalid syntax in a class body.
Even if it were allowed, the special constructor method for a class is named constructor, not the class name.
Therefore, only:
constructor(body, author, viewCount) {
correctly declares the constructor for the Story class and ensures instances created with new Story(body, author, viewCount) have all three properties populated.
Reference / Study Guide concepts (no links):
ES6 class syntax
constructor method in classes
this and instance properties in classes
Difference between class constructors and regular functions
Invalid use of super and function inside class bodies
________________________________________
NEW QUESTION # 137
Given the JavaScript below:
Which code should replace the placeholder comment on line 06 to hide accounts that do not match the search string?
Answer: A
NEW QUESTION # 138
......
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