The concept that allows JavaScript objects to inherit properties and behavior from an object of another class is known as _________.
- inheritance
- extension
- encapsulation
- polymorphism
The concept that allows JavaScript objects to inherit properties and behavior from an object of another class is known as "inheritance." Inheritance is a fundamental aspect of object-oriented programming and helps in code reusability.
What will happen if the break statement is omitted in a switch case?
- The program will continue to execute the following case(s) until a break or the end of the switch.
- It will skip the current case and move on to the default case.
- It will throw a syntax error.
- It will automatically add a break statement, preventing fall-through.
If you omit the break statement in a switch case, JavaScript will execute the code for that case and continue to execute the code for the following case(s) until it encounters a break statement or reaches the end of the switch statement. This behavior is known as "fall-through."
The keyword ______ is used to specify a block of code to be executed, if the same block that it is directly proceeding does not get executed.
- break
- continue
- return
- finally
The keyword finally is used to specify a block of code that will be executed regardless of whether an exception is thrown or not in a try...catch block. It ensures that cleanup code is always executed.
You are working on a web application where you need to fetch data from an API, perform operations on it, and then use it to update the UI. Which JavaScript feature allows you to handle these asynchronous operations more readably and reliably?
- Callback Functions
- Promises
- Event Loop
- Callback Hell
Promises in JavaScript allow you to handle asynchronous operations more readably and reliably. Promises provide a structured way to work with asynchronous code, making it easier to manage tasks like fetching data from an API, performing operations, and updating the UI when the data is ready.
Which keyword is used to declare a variable with block scope?
- let
- var
- const
- block
The let keyword is used to declare a variable with block scope in JavaScript. Variables declared with let are limited to the block or scope in which they are defined, which is typically within a pair of curly braces {}.
What will happen if the condition in a while loop is always true?
- The code block will never execute
- The code block will execute once
- An infinite loop will occur
- An error will be thrown
If the condition in a while loop is always true, an infinite loop will occur. The code block will keep executing repeatedly, and the loop will never exit. This can lead to the program becoming unresponsive, and it's essential to ensure that the condition in a while loop eventually becomes false to prevent infinite loops.
What is the impact on performance when using a switch statement versus multiple if-else statements for numerous conditions?
- Switch statements are generally faster than multiple if-else statements for numerous conditions because they use direct lookup tables.
- Switch statements are slower than multiple if-else statements for numerous conditions due to increased code complexity.
- There is no significant difference in performance between switch and if-else statements for numerous conditions.
- Switch statements are slower due to the need for explicit type conversions.
Using a switch statement is often more performant when dealing with numerous conditions because it uses direct lookup tables, making it faster and more efficient than a series of if-else statements, which involve sequential comparisons.
The comparison operator _______ checks for inequality, considering type coercion.
- ==
- ===
- !=
- !==
The comparison operator '!==' checks for inequality while also considering type coercion. It returns true if the values are not equal or if their types are not the same. For example, 5 !== "5" would evaluate to true because the number 5 is not equal to the string "5."
How does JavaScript implement inheritance internally?
- Through classes and interfaces
- Using a prototype chain and object delegation
- By creating abstract base classes
- Through function overloading
JavaScript implements inheritance through a prototype chain and object delegation. Each object has a prototype object, and if a property or method is not found on the object itself, it's looked up on the prototype chain. This mechanism allows objects to inherit properties and methods from their prototypes, facilitating code reuse and object-oriented programming in JavaScript. Classes and interfaces are not directly related to inheritance in JavaScript.
Which early browser first implemented JavaScript?
- Internet Explorer
- Mosaic
- Netscape Navigator
- Opera
JavaScript was first implemented in Netscape Navigator. Brendan Eich developed it in 1995 while working at Netscape Communications. This move by Netscape added a significant interactive element to the web and contributed to the rapid adoption of JavaScript.