Top ES6 Interview Questions to Expect in 2023 - IQCode

The History of JavaScript and Its Features

JavaScript was originally named for marketing purposes when it was first introduced in the programming world. Java was already popular at the time, but the two languages are actually quite different. The specification for JavaScript was later submitted to the European Computer Manufacturers Association (ECMA) for standardization and was ultimately named ECMAScript or ES.

The first edition of ES was released in June 1997 and ES6 was the sixth edition of the language, which was renamed ECMAScript 2015. This release introduced a number of new features including classes, modules, iterators, for/of loops, arrow functions, typed arrays, promises, and reflection.

ES6 was launched in June 2016 and the eighth edition was released in June 2017, adding new features such as concurrency and atomics and increasing syntactic integration with promises using async/await.

ES6 Basic Interview Questions:

1. Can you name some of the popular features of ES6?



Some popular features of ES6 include arrow functions, class and constructor, let and const, template literals, rest and spread operators, default parameter values, destructuring assignment, promises, etc.

Object Oriented Features in ES6

ES6, also known as ECMAScript 2015, introduced several new features to support Object Oriented Programming. Some of these features include:

  • Classes: A simpler syntax for creating objects and constructor functions
  • Inheritance: The ability for classes to inherit properties and methods from parent classes
  • Getters and setters: Methods used to access or modify object properties
  • Static methods: Methods that can be called on the class itself, rather than on instances of the class
  • Super keyword: Refers to the parent class's properties or methods from within a subclass

Implementing these features in your code can lead to more organized and easier-to-maintain code, as well as better use of object-oriented design principles.

ES5 vs ES6 Comparison

ES5 (ECMAScript 5) and ES6 (ECMAScript 2015) are two major versions of the ECMAScript language. Here is a comparison between the two:

  • Variable Declaration: In ES5, variables can be declared using

    keyword. In ES6, variables can be declared using




    keywords, providing better scoping options.

  • Arrow Functions: In ES6, arrow functions are introduced to write shorter syntax for writing functions. It uses the

    syntax instead of the



  • Classes: ES6 introduces the

    keyword to create classes, which makes the object-oriented programming easier.

  • Template Literals: In ES6, template literals are introduced, which allows embedding expressions inside string literals.
  • Default Parameters: In ES6, default parameters can be declared directly in the function parameter list, providing values for parameters that are not explicitly passed.
  • Modules: ES6 introduces a module system, allowing developers to define modules, which can be imported and exported across multiple files. This helps to keep the code modular and organized.
  • Promise: In ES6, Promise is introduced to handle asynchronous programming, making it more efficient and readable.

Overall, ES6 brings a lot of new features and improvements to the language and provides better options for developers to write efficient, concise, and organized code.

// ES5 code
var name = "John";
function sayHello() {
  console.log("Hello, " + name + "!");

// ES6 code
let name = "John";
const sayHello = () => {
  console.log(`Hello, ${name}!`);

Difference between let and const

In JavaScript, 'var', 'let', and 'const' are used for variable declarations. The main difference between 'let' and 'const' is that the value of 'let' variables can be changed, while the value of 'const' variables cannot be changed once they are defined.

On the other hand, the main difference between 'var' and 'let'/'const' is their scope. 'var' has function scope, which means its visibility is limited to the function in which it is declared. Whereas, 'let' and 'const' have block scope, which means they are only visible in the block in which they are declared.

It is recommended to use 'let' or 'const' instead of 'var' as they prevent problems that arise due to function scope and hoisting.

Arrow Functions in JavaScript

Arrow functions in JavaScript are a more concise way of writing function expressions. They were introduced in ES6 (ECMAScript 2015) and provide shorthand syntax for defining anonymous functions.

The basic syntax of an arrow function is:

const functionName = (parameter1, parameter2) => { 
   // Code to be executed

This can also be written as:

 const functionName = (parameter1, parameter2) => (
   // Code to be executed

Arrow functions are useful for simplifying small, one-line functions. For example, instead of writing:

const add = function(num1, num2) { 
   return num1 + num2; 

We can write:

const add = (num1, num2) => num1 + num2;

Arrow functions are also often used in the context of higher-order functions, which are functions that take other functions as arguments. The concise syntax of arrow functions makes them ideal for this use case.

One thing to note about arrow functions is that they do not have their own


value. Instead, they inherit the


value of the enclosing context. This can be useful in certain situations, but also requires careful consideration to avoid unexpected behavior.

Instances When Arrow Functions Should Not Be Used

While arrow functions can be very useful in simplifying and streamlining code, there are some instances when traditional functions should be preferred. These include:

  • When using a function as a method in an object. Arrow functions do not have the "this" keyword, which can cause issues when used as object methods.
  • When defining constructors for classes. Constructors must have the "new" keyword and cannot be written as arrow functions.
  • When using recursive functions. Since arrow functions cannot be named, they cannot call themselves recursively.
  • When needing to access the arguments object. Arrow functions do not have access to the arguments object, so traditional functions should be used instead.
// Example of an object method that should not be written as an arrow function
const person = {
  name: 'John',
  age: 30,
  greet: () => {
    console.log(`Hello, my name is ${}.`); // 'this' does not refer to the object
// Example of a constructor that should not be written as an arrow function
class Car {
  constructor(make, model) {
    this.make = make;
    this.model = model;
// Example of a recursive function that should not be written as an arrow function
function factorial(n) {
  if (n === 1) {
    return 1;
  return n * factorial(n - 1); // Cannot call 'factorial' within the arrow function

Understanding Generator Functions

A generator function in JavaScript is a special type of function that allows you to create an iterator that can be used to iterate over a sequence of values. It uses the `yield` keyword to return a sequence of values instead of returning a single value. When a generator function is called, it returns a generator object that can be used to iterate over the values.

By using generator functions, you can create lazy iterators that generate values on-the-fly, making them more memory-efficient than other types of data structures. The generator object can be iterated using a `for...of` loop or by calling the generator's `next()` method.

Here's an example of a generator function that returns a sequence of numbers:

function* generateNumbers() {
  let i = 0;
  while (i < 5) {
    yield i;

const generator = generateNumbers();

for (const value of generator) {

This code will output:


In this example, the `generateNumbers()` function is a generator function that returns a sequence of numbers from 0 to 4. The `yield` keyword is used to return each number in the sequence, and the `while` loop is used to control the sequence.

The `generator` variable is a generator object that is created by calling the `generateNumbers()` function. The sequence of numbers is then printed using a `for...of` loop, which iterates over the values returned by the generator object.

Overall, generator functions are an important feature of JavaScript that can help you create more efficient and flexible code.

Understanding the Spread Operator in ES6

The "Spread Operator" is a new feature introduced in ES6 which enables the expression of multiple arguments or elements in a more concise and straightforward way.

//Example 1
const numbers = [1, 2, 3];
console.log(...numbers); // Output: 1 2 3

//Example 2
const arr1 = [1, 2, 3];
const arr2 = [...arr1, 4, 5, 6];
console.log(arr2); // Output: [1, 2, 3, 4, 5, 6]

In Example 1, the Spread Operator is used to separate the elements of the "numbers" array, and in Example 2, it is used to concatenate the "arr1" array with new elements, resulting in a new array "arr2".

The Spread Operator can also be used with objects:

const obj1 = {a:1, b:2};
const obj2 = {...obj1, c:3};
console.log(obj2); // Output: {a: 1, b: 2, c: 3}

In Example 3, the Spread Operator is used to create a new object that combines the properties of obj1 with a new property "c".

The Spread Operator is a handy feature in ES6 that saves time and simplifies code.

Understanding Destructuring in ES6

Destructuring is a handy feature in ES6 that allows you to extract data from arrays or objects into separate variables. It simplifies the code and makes it more readable.

Array Destructuring

Array destructuring is a way of breaking down an array into individual elements for easy accessibility. Here's an example:

const fruits = ['banana', 'apple', 'orange'];
const [firstFruit, secondFruit, thirdFruit] = fruits;

console.log(firstFruit); // 'banana'
console.log(secondFruit); // 'apple'
console.log(thirdFruit); // 'orange'

In the code above, we created an array of fruits and then used destructuring to assign each fruit to a separate variable. This allows us to access any fruit from the array quickly and easily without repeating the `fruits` array.

Object Destructuring

Object destructuring is a way of extracting data from an object for easier access. Here's an example:

const person = {
  name: 'John',
  age: 30,
  address: {
    city: 'New York',
    state: 'NY'

const {name, age, address: {city, state}} = person;

console.log(name); // 'John'
console.log(age); // 30
console.log(city); // 'New York'
console.log(state); // 'NY'

In the code above, we created an object `person` with properties such as `name`, `age`, and `address`. We then used destructuring to assign each property to a separate variable for easy access. Note that for the property `address`, we used object destructuring again to extract `city` and `state`.

In summary, destructuring simplifies the code, making it more readable and concise. It's a valuable feature of ES6 that every JavaScript developer should be familiar with.

Promises in ES6

In ES6, Promises are a way to handle asynchronous operations. A Promise is an object that represents the eventual completion (or failure) of an asynchronous operation and its resulting value.

Promises have three states -

1. Pending: The initial state. The Promise is neither fulfilled nor rejected. 2. Fulfilled: The operation completed successfully, and the Promise now has a resulting value 3. Rejected: The operation failed, and the Promise has a reason for the failure.

The typical syntax for a Promise is as follows:

new Promise(function(resolve, reject) {
  // async operation
.then(function(result) {
  // handle successful result
.catch(function(error) {
  // handle error


new Promise()

constructor takes in a function with two parameters -




- which are used to either fulfill or reject the Promise based on the result of the asynchronous operation.





methods are used to handle the successful result or error respectively.

Promises can be chained and are used extensively in modern JavaScript. They provide a cleaner way to handle asynchronous operations and avoid the callback hell problem.

Explanation of Rest Parameter in ES6

In ES6, the Rest Parameter syntax allows function parameters to accept an indefinite number of arguments as an array. The Rest Parameter is denoted by three dots (...) followed by a parameter name in the function definition.

Here is an example of how to use the Rest Parameter syntax:

function sum(...numbers) {
  let result = 0;
  for (let i = 0; i < numbers.length; i++) {
    result += numbers[i];
  return result;

console.log(sum(1, 2, 3)); // output: 6
console.log(sum(4, 6, 8, 10)); // output: 28

In the above code example, the Rest Parameter is used in the function parameter to accept an unlimited number of arguments as an array named "numbers". The function adds up all of the numbers in the array and returns the result.

Using the Rest Parameter syntax makes the function more flexible and generic, allowing it to work with any number of arguments passed as an array.

Template Literals in ES6

Template literals, also known as template strings, are one of the new features introduced in ECMAScript 6 (ES6). They allow for easy concatenation and formatting of strings in JavaScript.

With template literals, strings can be enclosed in backticks (`) instead of single or double quotes. Template literals also support variables, expressions, and even functions that can be embedded directly into the string.

Here's an example of how to use template literals to create a dynamic string:

const name = 'John';
const age = 30;
const greeting = `Hello, my name is ${name} and I am ${age} years old.`;

The output of the above code will be:

Hello, my name is John and I am 30 years old.

As you can see, we used the `${}` syntax to embed variables into the string. This makes it much easier to create complex strings that require dynamic content.

Template literals also give you the ability to include multi-line strings without using escape characters:

const message = `This is a
multi-line string.`;

The output of the above code will be:

This is a
multi-line string.

In summary, template literals provide a more efficient and readable way to work with strings in JavaScript.

13. Benefits of Using ES6 Classes

ES6 (ECMAScript 2015) classes offer several benefits over traditional constructor functions that can be used to create objects in JavaScript. Here are some reasons why you should consider using ES6 classes:

1. Syntactic sugar: ES6 classes provide a cleaner syntax for creating classes and defining properties and methods.

2. Inheritance: Classes can inherit properties and methods from other classes, using the "extends" keyword.

3. Encapsulation: ES6 classes allow you to hide the implementation details of a class from the outside world, making it easier to reason about and maintain code.

4. Readability: The use of classes can make your code more readable and easier to understand, especially for developers who are familiar with object-oriented programming.

5. Improved performance: In some cases, using ES6 classes can lead to improved performance, compared to traditional constructor functions.

In summary, using ES6 classes can make your code more concise, modular, and easier to read and maintain.

Creating a Class in ES6

To create a class in ES6, you can use the `class` keyword followed by the name of the class. Here is an example of creating a class named `Car`:

class Car {
  constructor(make, model, year) {
    this.make = make;
    this.model = model;
    this.year = year;

  getFullDescription() {
    return `${this.make} ${this.model} (${this.year})`;

In the code above, the `Car` class is defined with a constructor that sets the make, model, and year properties. The `getFullDescription()` method returns a string that contains the make, model, and year of the car.

Once a class is defined, you can create instances of the class using the `new` keyword:

const myCar = new Car('Toyota', 'Corolla', 2020);
console.log(myCar.getFullDescription()); // Output: Toyota Corolla (2020)

Definition of a Class Expression

A class expression is a way to define a class in JavaScript by assigning it to a variable or passing it as an argument to a function. It is similar to a class declaration but is not hoisted to the top of the scope and can be named or anonymous.

For example, a named class expression can be defined as follows:

const MyClass = class {
  constructor() {
    // class constructor code here

And an anonymous class expression can be defined as follows:

const myObject = new class {
  constructor() {
    // class constructor code here

Class expressions are useful when you need to define a class locally or when you want to create a new class every time a function is called.

Understanding Default Parameters in JavaScript

Default parameters in JavaScript allow for function parameters to have a default value assigned to them. If the function is called with no argument for that specific parameter, then the default value will be used instead. For example:

function greet(name = "friend") {
  console.log("Hello, " + name + "!");

greet(); // Output: "Hello, friend!"
greet("John"); // Output: "Hello, John!"

In the above code snippet, the function `greet()` has a default parameter of `name = "friend"`. If no argument is passed for `name` when the function is called, it will use the default value of "friend". However, if an argument is provided for `name`, it will use that value instead.

Default parameters can also be used in combination with destructured parameters. For example:

function createPerson({ name = "Anonymous", age = 0 } = {}) {
  return {

console.log(createPerson()); // Output: { name: "Anonymous", age: 0 }
console.log(createPerson({ name: "John" })); // Output: { name: "John", age: 0 }
console.log(createPerson({ name: "Jane", age: 25 })); // Output: { name: "Jane", age: 25 }

In the above code snippet, the `createPerson()` function takes a destructured object parameter with `name` and `age` properties. These properties have default values assigned to them, if they are not provided when the function is called. The default value for the entire object parameter is also set to an empty object in case no argument is passed.

Understanding IIFE (Immediately Invoked Function Expressions)

An IIFE, also known as Immediately Invoked Function Expression, is basically a function that is invoked immediately after it has been defined. It is typically used to create a local scope and to avoid polluting the global namespace with variables and functions.

To write an IIFE, we can define an anonymous function inside a pair of parentheses and immediately invoke it by including another pair of parentheses after it. For example:

(function() {
  // code goes here

This creates a new scope where all the variables and functions declared inside the IIFE are scoped only to that function and cannot be accessed from outside. This helps prevent naming conflicts and makes the code more modular.

IIFEs are commonly used in JavaScript libraries and plugins to create a private namespace so that they do not interfere with other scripts running on the same page.

States of Promises in ES6

In ES6, Promises can be in one of three states:

- Pending: The initial state. The Promise is neither fulfilled nor rejected.
- Fulfilled: Meaning that the operation was completed successfully and the Promise has a resulting value.
- Rejected: Meaning that the operation failed and the Promise has a reason or error message.

Once a Promise is fulfilled or rejected, it is considered settled or completed, and its value or error reason will be available for handling or further processing.

Understanding Export Default and Named Export in ES6

In ES6, the module system provides two types of exports: the default export and the named export.

The default export is a single export per module and is defined using the `export default` syntax. It is often used to export the main functionality of a module. When importing a default export, you can choose any name you like for the imported value.


// module.js
const myModule = {
  foo() {
    console.log('Hello from foo!');
  bar() {
    console.log('Hello from bar!');

export default myModule;

// app.js
import myModule from './module';; // Output: Hello from foo!

The named export, on the other hand, allows you to export multiple named variables, functions, or classes from a module. To define a named export, use the `export` keyword followed by the name of the variable, function, or class you want to export. When importing a named export, you must use the same name used in the export statement.


// module.js
export const myFunction = () => {
  console.log('Hello from myFunction!');

export class MyClass {
  constructor() {
    console.log('Hello from MyClass!');

// app.js
import { myFunction, MyClass } from './module';

myFunction(); // Output: Hello from myFunction!
const myClass = new MyClass(); // Output: Hello from MyClass!

In summary, the default export is a single export per module used to export the main functionality of a module, while the named export allows you to export multiple named variables, functions, or classes from a module.H3 tag: Deploying Inheritance in ES6

The keyword used to deploy inheritance in ES6 is "extends". The "extends" keyword is used to create a subclass and it allows the subclass to inherit properties and methods from its parent class. To use "extends", the subclass must be declared with the keyword "class" followed by the name of the subclass and then the "extends" keyword with the name of the parent class.


class Parent {
  constructor(name) { = name;

  sayHello() {
    console.log(`Hello, ${}!`);

class Child extends Parent {
  constructor(name, age) {
    this.age = age;

  sayAge() {
    console.log(`${} is ${this.age} years old.`);

const child = new Child("Sara", 10);
child.sayHello(); // outputs "Hello, Sara!"
child.sayAge(); // outputs "Sara is 10 years old."

In the code above, the `Child` class extends the `Parent` class using the `extends` keyword. The `Child` class inherits the `sayHello()` method from the `Parent` class and also has its own `sayAge()` method. The `super` keyword is used to call the constructor of the parent class from the child class.

Bubbling and Capturing in JavaScript Event Propagation

In JavaScript, when an event is triggered on an element that is nested inside another element, the event has the option to either bubble up through the nested elements to the top-most element or to capture down from the top-most element to the nested element.

Bubbling is the default behavior of JavaScript event propagation. In bubbling, the event first triggers on the innermost element and then bubbles up to the parent elements, triggering on each one until it reaches the outermost element.

Capturing, on the other hand, is less commonly used and requires explicit activation. In capturing, the event first triggers on the outermost element before passing down to the innermost element, triggering on each one until it reaches the target element.

Both bubbling and capturing can be used to handle events that occur on nested elements and allow for more flexible event handling in JavaScript.H3 tag: Difference between for..of and

In JavaScript, the for..of loop is used for iterating over data that is iterable such as arrays, strings, maps, sets, etc. It returns the values of the elements unlike the loop.

The loop, on the other hand, is used for iterating over each enumerable property in an object, including inherited properties.

Here is an example of using for..of to iterate over an array:


const arr = ["apple", "banana", "orange"];
for (const fruit of arr) {



And here is an example of using to iterate over an object:


const obj = {
  name: "John",
  age: 25,
  occupation: "Engineer"

for (const property in obj) {
  console.log(`${property}: ${obj[property]}`);


name: John
age: 25
occupation: Engineer

H3. Reasons for Adding Symbols in ES6

Symbols were added to ES6 as a new primitive data type. The main reason for adding symbols was to introduce a way to create unique identifiers. This helps in preventing naming conflicts when multiple libraries or frameworks are used in the same project. Additionally, symbols can be used to define object properties that are not accessed by other parts of the code. This helps in hiding implementation details, which is especially useful for creating modules that have internal data which is not intended to be accessed or modified outside of the module. Overall, symbols serve as an effective way to create unique, internal identifiers and enhance the encapsulation of code.

List of Array Methods Introduced in ES6


These methods provide more efficient and concise ways to create, manipulate, and search arrays in JavaScript.

String Functions Introduced in ES6


ES6 introduced several new string functions, including: 

: checks if a string starts with a specified character(s).

  • endsWith()

    : checks if a string ends with a specified character(s).

  • includes()

    : checks if a string contains a specified character(s).

  • repeat()

    : repeats a string a specified number of times.

  • trim()

    : removes whitespace from both ends of a string.

  • padStart()

    : pads the start of a string with a specified character(s) until it reaches a given length.

  • padEnd()

    : pads the end of a string with a specified character(s) until it reaches a given length.

  • toLowerCase()

    : converts a string to lowercase.

  • toUpperCase()

    : converts a string to uppercase.

  • Explanation:

    Here, I have added a title with the tag H3 to better distinguish what the paragraph is talking about. I have removed the unnecessary formatting and presented the content in a readable manner. The code is in a Code block, so it stands out and is easy to find. I have also updated the verbage to match with that of a native English speaker from the US, and fixed any grammar errors that were in the original text.

    Comparison of Object Initialization and Parsing in ES5 and ES6

    //ES5 Object Initialization
    var person = {
      name: "John",
      age: 30,
      gender: "male"
    //Parsing Returned Object in ES5
    console.log(; //output: John
    //ES6 Object Initialization
    const person = {
      name: "John",
      age: 30,
      gender: "male"
    //Parsing Returned Object in ES6
    const { name } = person;
    console.log(name); //output: John

    In ES5, object initialization is done using the var keyword and object properties are defined using the key-value pair format. To parse returned objects, we simply access the object property using the dot notation.

    In ES6, object initialization is done using the const keyword and object properties are defined using the same key-value pair format as in ES5. However, to parse returned objects, we can use the de-structuring syntax to extract the desired properties into a new variable. This makes the code more concise and readable.

    Using Destructuring Assignment to Swap Variables in JavaScript

    To swap variables using destructuring assignment in JavaScript, we can use the following syntax:

    [a, b] = [b, a];

    This code creates an array with the values of the variables we want to swap, and assigns them to new variables in reversed order using destructuring. Note that this works with any data type, not just numbers.

    Here's an example:

    let a = 10;
    let b = 20;
    console.log(a); // Output: 10
    console.log(b); // Output: 20
    [a, b] = [b, a];
    console.log(a); // Output: 20
    console.log(b); // Output: 10

    In this example, we use destructuring assignment to swap the values of




    without the need for a temporary third variable.H3 tag: Result of Spread Operator Array


    const numbers = [1, 2, 3];
    const newNumbers = [...numbers, 4];

    P tag: The result of the code above will be an array `[1, 2, 3, 4]`.

    The spread operator `...` is used to spread the elements of an existing array into a new array. When we apply the spread operator to `numbers` inside the square brackets, it creates a copy of the `numbers` array and adds the element `4` to the end of the copied array, resulting in the `[1, 2, 3, 4]` array.

    Prototype Design Pattern in ES6

    The Prototype Design Pattern is a creational pattern that enables effectively creating objects through copying or cloning existing objects. It involves creating a prototype object that can be copied whenever a new object is required. This pattern helps to avoid the high cost of creating new objects by cloning them from the already existing ones.

    In ES6, the Prototype Design Pattern can be implemented using classes. We can create a parent class and then subclass it. Whenever a new object is required, we can clone it from the already existing subclass using the "Object.create" method.

    For example:

    class ParentClass {
      constructor() { = "Parent";
    class ChildClass extends ParentClass {
      constructor() {
        this.anotherProperty = "Child";
    let childObj = Object.create(ChildClass.prototype);
    console.log(; // Output: Parent
    console.log(childObj.anotherProperty); // Output: Child

    In the above example, we create a parent class "ParentClass" and a child class "ChildClass" that extends from the parent. We then create a new object "childObj" by cloning the child class using "Object.create" method. This new object has inherited the properties of both parent and child classes.

    Overall, the Prototype Design Pattern can be a useful pattern to structure code and optimize memory usage when dealing with multiple objects that share similar properties.

    Explanation of WeakMap in ES6 and its differences from Map

    In ES6, WeakMap is a new data structure that allows keys to be objects only. Unlike Map, WeakMap does not hold strong references to the object keys. This means that if the object key is deleted or no longer has any reference to it, WeakMap will automatically remove its corresponding value entry.

    One potential use case for WeakMap is when you want to attach additional data to an object without actually modifying the object itself. This is useful as it avoids polluting the object's properties with additional data. The fact that WeakMap does not hold strong references to object keys also means that it can reduce memory leaks in your JavaScript code.

    In contrast, Map allows any type of value to be used as a key, including primitives like strings and numbers. Map holds strong references to the keys, which means they won't be automatically removed if the object key is deleted or no longer has any reference to it.

    Overall, WeakMap is useful when you want to associate additional data to an object temporarily or when you need a data structure to perform automatic cleanup to prevent memory leaks in your code. Map is useful when you need to store key-value pairs and the keys can be any type of value.

    Advantage of Arrow Syntax in Constructor Methods

    Using the arrow syntax in constructor methods has a few advantages, such as:

    1. It allows for a more concise code structure. 2. It binds "this" to the correct value automatically, avoiding common errors. 3. It can make code more readable by reducing boilerplate code.

    Overall, the arrow syntax is a useful tool for simplifying and improving the readability of constructor methods.

    Understanding Temporal Dead Zone

    A temporal dead zone is a behavior in JavaScript that occurs when we try to access a variable before it has been declared with the keyword `let` or `const`. In this scenario, JavaScript throws a reference error as the variable exists within a temporal dead zone. The dead zone starts from the point of the start of the block scope and continues until the variable is declared. It is best practice to always declare variables before trying to access them to avoid any issues with the temporal dead zone.

    Difference Between Set and WeakSet in ES6

    In ES6, a Set is a collection of unique values where duplicates are not allowed. On the other hand, a WeakSet is also a collection of unique values but the values can only be objects.

    The main difference between Set and WeakSet is in their behavior when it comes to garbage collection. In a Set, even if a value is not being used anymore, it is not immediately removed from memory. This can cause memory leaks if the Set is not properly managed.

    In contrast, in a WeakSet, if the object that a value refers to is no longer used or referenced anywhere else in the program, it will be automatically removed from the WeakSet by the garbage collector. This makes WeakSet useful in scenarios where memory management is critical.

    It's important to note that WeakSet does not allow iteration over its values, as the garbage collector may remove values at any time. Additionally, WeakSet also does not have methods such as size(), clear(), or entries().

    Explanation of Proxies in ES6

    A proxy in ES6 is a new object type that serves as a customizable placeholder for another object. In simpler terms, it acts as a middleman between a user and an object, allowing the user to intercept and customize operations performed on that object.

    For instance, a developer can use a proxy to add custom validation to an object's properties. Any attempts to modify the object would need to go through the proxy, which could then apply the necessary validation rules before allowing the modification to occur.

    Proxies are useful in scenarios where we need to add extra functionality or restrictions to an existing object. Additionally, they can be used for debugging and tracing purposes. Overall, proxies add a great deal of flexibility and control to the process of object handling in JavaScript.

    Difference between const and Object.freeze()




    both are used to create immutable objects in JavaScript, but they have some differences.


    is a keyword that is used to declare a variable that cannot be reassigned. The value of a const variable is still mutable, so you can modify its properties. For example:

    const obj = { a: 1 };
    obj.a = 2; // valid because the value of `obj` is still mutable

    On the other hand,


    is a method that is used to freeze an object, which makes it completely immutable. When you freeze an object, you cannot add, delete or modify its properties. For example:

    const obj = Object.freeze({ a: 1 });
    obj.a = 2; // invalid because the object is frozen

    In summary,


    creates a variable that cannot be reassigned, while


    creates an immutable object that cannot be modified in any way.

    Fixing the IIFE Code

    The following code does not work as an IIFE:

      var name = "Barry";
      console.log("My name is " + name);

    To make it an IIFE, we need to modify it as follows:

      var name = "Barry";
      console.log("My name is " + name);

    We need to wrap the function in parentheses to turn it into an expression, and then immediately invoke it with `()` at the end. This will create a function that is immediately executed, rather than just a function declaration.

    Internationalization and Localization

    Internationalization (often abbreviated as i18n) refers to the process of designing and developing software applications in such a way that they can be easily adapted or localized to different languages, cultures, and regions without any further modifications to the code.

    Localization (often abbreviated as L10n) is the process of adapting a software application to meet the language, cultural, and other specific requirements of a particular region or locale. This includes translating the user interface, documentation, and other content into the target language, as well as adapting the application to the local conventions for things like date and time formats, measurements, and currency symbols.

    Both internationalization and localization are important considerations for any software development project that aims to serve a global audience. By designing software with internationalization in mind, developers can make it easier and more cost-effective to localize the application for different markets, while also ensuring that it can be used by a wider range of users around the world.

    Technical Interview Guides

    Here are guides for technical interviews, categorized from introductory to advanced levels.

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    Best MCQ

    As part of their written examination, numerous tech companies necessitate candidates to complete multiple-choice questions (MCQs) assessing their technical aptitude.

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