Mastering JavaScript: A Comprehensive Guide to Its History and Interview Questions with Tabular Differences

Introduction:

JavaScript is a high-level programming language that is used to make web pages interactive and dynamic. It is the most popular language on the web, and is widely used for front-end and back-end web development. JavaScript was created in 1995 by Brendan Eich, and has since become one of the most important languages in modern web development. In this post, we will explore the history of JavaScript, and provide some interview questions with tabular differences that can help you better understand the language.

History of JavaScript:

JavaScript was created in 1995 by Brendan Eich, while he was working at Netscape Communications Corporation. Eich was tasked with creating a language that could be used to add interactivity to web pages. He created a prototype of the language in just 10 days, and it was first released as part of the Netscape Navigator 2.0 browser in September of that year. Originally, the language was called Mocha, but it was later renamed to LiveScript, and then finally to JavaScript.

JavaScript was quickly adopted by other web browsers, and became a de facto standard for client-side scripting on the web. In 1996, Microsoft created a rival language called JScript, which was designed to be compatible with JavaScript but had a few differences. The two languages were eventually standardized by the ECMA International organization, which created the ECMAScript standard.

The first version of ECMAScript was released in 1997, and it included the core features of the language, such as variables, functions, and loops. Over the years, new versions of ECMAScript have been released, each adding new features and improving the language. The most recent version of ECMAScript is ECMAScript 2022, which was released in June 2022.

Interview Questions with Tabular Differences:

To help you better understand JavaScript, we have compiled a list of interview questions with tabular differences. These questions cover a range of topics, from the basics of the language to more advanced concepts.

1. What is the difference between var, let, and const in JavaScript?

var	let	const
Function-scoped	Block-scoped	Block-scoped
Can be redeclared	Cannot be redeclared	Cannot be redeclared
Can be reassigned	Can be reassigned	Cannot be reassigned

2. What is the difference between == and === in JavaScript?

==	===
Loose equality comparison	Strict equality comparison
Does type coercion	Does not do type coercion
"1" == 1 is true	"1" === 1 is false

3. What is the difference between a function declaration and a function expression in JavaScript?

Function declaration	Function expression
Can be called before it is defined	Must be defined before it is called
Starts with the keyword function	Can start with any expression that evaluates to a function
Has a name	Can be anonymous

4. What is the difference between synchronous and asynchronous code in JavaScript?

Synchronous code	Asynchronous code
Executes in a single thread	Executes in multiple threads
Blocks the execution until it completes	Does not block the execution
Easy to reason about	Difficult to reason about

5. What is the difference between callback, promise, and async/await in JavaScript?

Callback	Promise	Async/await
Uses a function as a parameter	Returns a promise object	Uses the async and await keywords
Callback hell can occur	No callback hell	No callback hell
Difficult to read and understand	Easier to read and understand than

6. What is the difference between null and undefined in JavaScript?

null	undefined
A value that represents the absence of any object value	A value that represents the absence of any value
Can be explicitly set	Is the default value of uninitialized variables
typeof null returns "object"	typeof undefined returns "undefined"

7. What is the difference between a for loop and a for...in loop in JavaScript?

for loop	for...in loop
Used to iterate over arrays and objects with known length	Used to iterate over object properties
Uses a counter to keep track of the current index	Uses a variable to store the current property name
Can be used with break and continue statements	Should not be used with break and continue statements

8. What is the difference between call() and apply() methods in JavaScript?

call() method	apply() method
Takes individual arguments as parameters	Takes an array of arguments as a parameter
Used to invoke a function with a specified context	Used to invoke a function with a specified context
function.call(context, arg1, arg2, ...)	function.apply(context, [arg1, arg2, ...])

9. What is the difference between the spread operator and the rest parameter in JavaScript?

Spread operator	Rest parameter
Used to spread the elements of an array or object	Used to gather all remaining arguments into an array
Used in function calls and array literals	Used in function parameters
...[1, 2, 3] returns 1, 2, 3	function(...args) {...}

10. What is the difference between a class and a constructor function in JavaScript?

Class	Constructor function
Introduced in ES6	Pre-ES6 way of creating objects
Can use class inheritance and static methods	Cannot use class inheritance or static methods
Uses the keyword "class" to define a template	Uses a function and "new" keyword to create an object
class Person {...}	function Person(...) {...}

11. What is the difference between a closure and a callback function in JavaScript?

Closure	Callback function
A function that has access to variables in its outer scope	A function that is passed as an argument to another function and is invoked when a specific event occurs
Used for data hiding, encapsulation, and to create private variables	Used to handle asynchronous operations and events
function outer() { let x = 10; function inner() { console.log(x); } return inner; }	function fetchData(url, callback) { fetch(url).then(response => callback(response)); }

12. What is the difference between synchronous and asynchronous code execution in JavaScript?

Synchronous code	Asynchronous code
Code that executes one line at a time, in the order it appears in the program	Code that executes out of order, based on the completion of a specific event or task
Can cause the program to "block" if a long-running operation is performed	Does not block the program, allowing other operations to be performed concurrently
function sync() { console.log("start"); longRunningOperation(); console.log("end"); }	function async() { console.log("start"); setTimeout(() => { console.log("timeout"); }, 1000); console.log("end"); }

13. What is the difference between an arrow function and a regular function in JavaScript?

Arrow function	Regular function
Introduced in ES6	Pre-ES6 way of defining functions
Does not have its own "this" context	Has its own "this" context
Cannot be used as a constructor	Can be used as a constructor
(x, y) => x + y	function add(x, y) { return x + y; }

14. What is the difference between let and var in JavaScript?

let	var
Introduced in ES6	Pre-ES6 way of declaring variables
Has block scope	Has function scope
Cannot be redeclared in the same scope	Can be redeclared in the same scope
let x = 10;	var x = 10;

15. What is the difference between a promise and an observable in JavaScript?

Promise	Observable
Used to handle asynchronous operations	Used to handle streams of asynchronous data
Can only return a single value or an error	Can return multiple values over time
Promise.resolve(42).then(value => console.log(value));	const observable = new Observable(observer => { observer.next(1); observer.next(2); observer.next(3); });

Conclusion:

By preparing for JavaScript job interviews with these interview questions with tabular differences, you can deepen your knowledge of the language and be better equipped to answer technical questions about its features and concepts. JavaScript is a powerful and widely used language that is constantly evolving