Basic JavaScript MCQ

A block of statements is a group of zero or more statements that are treated as a single unit.
In JavaScript, a block of statements is defined using curly braces {}.
A block of statement can be understand as the set of the zero or more statements.
In general, a block of statement has common definition "which combines one or a number of statements into a single statement for ease.

You can use the javascript: protocol in a URL to execute a JavaScript function.
This can be used, for example, to create a link that executes a JavaScript function when clicked.

For functions expressed as expressions, the function name is optional in Javascript. A function expression may be defined and used in the same way.

The substr() method extracts a specified number of characters from a string,
starting at a specified index position.
Here's an example of how to use it:
let str = 'Hello World';
let sub = str.substr(6, 5); // Extract 5 characters starting at index 6
console.log(sub); // Output: "World"
The substr() method is similar to the substring() method, which also extracts characters from a string.
The main difference between the two is that substring() does not allow negative indexes, whereas substr() does.

The === operator is known as the strict equality operator in JavaScript.
It is used to test whether two values are equal, and it returns true if the values are equal and their types are the same.

For example:
console.log(1 === 1); // Output: true
console.log('1' === 1); // Output: false

In the first example, the === operator returns true because both operands are equal and have the same type (number).
In the second example, the === operator returns false because although the operands are equal in value, they have different types (string and number).
The strict equality operator is often used as an alternative to the == operator, which is known as the abstract equality operator.
The == operator performs type coercion, which means it converts the operands to the same type before making the comparison.
This can lead to unexpected results in some cases, so the === operator is generally considered a safer choice.

The == operator is known as the abstract equality operator in JavaScript, and it is used to test whether two values are equal.
The operator converts the operands to the same type before making the comparison, so it can return true even if the operands have different types.
For example:

console.log(1 == 1); // Output: true
console.log('1' == 1); // Output: true


In the first example, the == operator returns true because both operands are equal and have the same type (number).
In the second example, the == operator returns true because although the operands have different types (string and number),
they are equal in value after being converted to the same type.
The != operator, on the other hand, is the non-equality operator. It tests whether two values are not equal,
and it returns true if the values are not equal or their types are not the same.
For example:

There are several ways to convert a value to a string in JavaScript.
Here are a few examples:
value.toString():
This method is available on many JavaScript objects and it returns a string representation of the object.
For example:
let x = 123;
console.log(x.toString()); // Output: "123"
let y = true;
console.log(y.toString()); // Output: "true"
"" + value:
This is known as string concatenation,
and it converts the value to a string by concatenating it with an empty string.
For example:
let x = 123;
console.log("" + x); // Output: "123"

let y = true;
console.log("" + y); // Output: "true"
String(value):
This is the String constructor, and it converts the value to a string by calling the toString() method on it.
For example:
let x = 123;
console.log(String(x)); // Output: "123"

let y = true;
console.log(String(y)); // Output: "true"<
All of these methods can be used to convert a value to a string without using the new operator.

If this code is run, the function will return true.
The == operator, also known as the abstract equality operator, compares two values for equality.
It converts the operands to the same type before making the comparison, so it can return true even if the operands have different types.
In this case, the variable x is of type int (integer) and the variable y is of type char (character).
However, the == operator will convert both variables to the same type (number) before making the comparison, so the comparison will evaluate to true.
If you wanted to perform a strict comparison that only returns true if the operands are equal and have the same type,
you could use the === operator instead.

A function definition expression, also known as a function literal, is a way to define a function in JavaScript.
It consists of the function keyword, followed by a list of parameters inside parentheses,
and a block of code inside curly braces that defines the function's behavior.
Here's an example of a function definition expression:
let greet = function(name) {
console.log('Hello, ' + name);
};

This function definition expression defines a function called greet that takes a single parameter called name and logs a greeting to the console.

The subset excludes the comma operator, bitwise operators, and the ++ and — operators.
Additionally, it requires the use of == and!= instead of == and!= owing to the type conversion that they do.

Global variables are variables that are defined outside of any function or block of code.
They have global scope, which means that they are visible and can be accessed from anywhere in your code.

Here's an example of how to define a global variable in JavaScript:
let x = 5; // x is a global variable
function foo() {
console.log(x); // x is visible and can be accessed from within the function
}

foo(); // Output: 5

It is generally considered a best practice to avoid using global variables in your code,
as they can lead to conflicts and make your code harder to maintain. Instead, it is usually better to use local variables that are defined within a function or block of code,
and to pass data between functions as arguments and return values.

In JavaScript, if a local variable and a global variable have the same name, the local variable takes precedence over the global variable.
Here's an example of how this works:
let x = 5; // x is a global variable
function foo() {
let x = 10; // x is a local variable
console.log(x); // Output: 10
}

foo(); // Output: 10
console.log(x); // Output: 5
In this example, the local variable x is defined within the foo function, and it takes precedence over the global variable x.
When we log the value of x within the function, it prints 10, which is the value of the local variable.
When we log the value of x outside the function, it
prints 5, which is the value of the global variable.

This is known as variable shadowing,
and it occurs when a local variable with the same name as a global variable "shadows" the global variable, hiding it from view within the local scope.

There are several ways to get a reference to an HTML element in JavaScript:
getElementById():
This method is used to get a reference to an element with a specific id.
For example:
let element = document.getElementById('my-element');
getElementsByClassName():
This method is used to get a list of elements with a specific class name.
For example:
let elements = document.getElementsByClassName('my-class');

In this code, we are using a for loop to iterate over a range of values, and we are using the setTimeout() function to log the value of i to the console after a delay of 1 millisecond.
However, the setTimeout() function runs asynchronously, which means that it does not block the rest of the code from executing.
This means that the for loop will complete immediately, and the value of i will be incremented to 3.
Since the setTimeout() function has a delay of 1 millisecond, it will not run until after the for loop has completed.
By the time the setTimeout() function runs, the value of i will already be 3, so it will log 3 to the console three times.

Laravel is not a JavaScript framework.
Laravel is a PHP framework for web application development. It provides a set of tools and libraries for building web applications using the PHP programming language.

Vue, React, and Node are all JavaScript frameworks.
Vue is a progressive JavaScript framework for building user interfaces.
React is a JavaScript library for building user interfaces.
Node is a JavaScript runtime that allows you to run JavaScript on the server side.

The let and var keywords are known as declaration statements or variable declarations.
A declaration statement is a statement in JavaScript that declares a variable or function.
The let and var keywords are used to declare variables in JavaScript.
Here are some examples of declaration statements:
let x; // Declares a variable x with the let keyword
var y; // Declares a variable y with the var keyword

function foo() { // Declares a function foo with the function keyword
// Function body }

The onkeydown, onkeypress, and onkeyup events are all related to the keyboard in JavaScript.
The onkeydown event is triggered when a user presses a key on the keyboard.
The onkeypress event is triggered when a user presses and releases a key on the keyboard.
The onkeyup event is triggered when a user releases a key on the keyboard.
Here's an example of how you might use these events in your code:

document.addEventListener('keydown', function(event) {
console.log('Keydown event:', event);
});

document.addEventListener('keypress', function(event) {
console.log('Keypress event:', event);
});

document.addEventListener('keyup', function(event) {
console.log('Keyup event:', event);
});

The onfocus event, on the other hand, is related to an element on the page receiving focus. It is triggered when an element receives focus, either by a user clicking on it or tabbing to it using the keyboard.

Here's an example of how you might use the onfocus event:

let input = document.querySelector('input');

input.addEventListener('focus', function() {
console.log('Input received focus');
});

In JavaScript, let arr = []; is the correct way to create a new array.
This is known as an array literal, and it is the most concise and commonly used way to create an array in JavaScript.

An array literal is a simple way to create an array by enclosing a list of values in square brackets ([]).
Each value in the list is called an element of the array, and the elements are separated by commas.

For example, the following code creates an array of numbers:

let arr = [1, 2, 3, 4, 5];

The following code creates an array of strings:

let arr = ['a', 'b', 'c', 'd', 'e'];

And the following code creates an array of mixed data types:

let arr = [1, 'a', true, {}, []];

arr[3] is the correct way to access the third element in an array arr.
In JavaScript, you can use square brackets ([]) to access elements in an array by their index.
The index of the first element in an array is 0,
so to access the third element, you would use an index of 2.

obj.newProperty = 'value'; is the correct way to add a new property to an object in JavaScript.
You can use the dot notation (obj.property) or the square bracket notation (obj['property']) to add a new property to an object.

The result of the code is true.
The == operator in JavaScript performs type coercion, which means that it converts the operands to the same type before performing the comparison.
In this case, the string '10' is converted to the number 10, so the comparison returns true.

The result of the code is false.
The === operator in JavaScript performs a strict comparison, which means that it not only checks for equality,
but also checks for type equality.
In this case, the operands x and y have different types (one is a number and the other is a string), so the comparison returns false.

The result of the code is 'object'.
In JavaScript, the typeof operator returns a string that represents the type of a value.
However, the typeof operator has a few quirks,
one of which is that it returns 'object' for null values.
This is a known issue in JavaScript, and it can cause confusion for developers who are not aware

in is not a logical operator in JavaScript.
Logical operators in JavaScript include && (and), || (or), and ! (not).
in is an operator that is used to check whether an object has a property with a given name.

The result of the code is 25.
In JavaScript, the * operator performs multiplication if both operands are numbers.
In this case, the string '5' is coerced to the number 5, so the final result is 5 * 5 = 25