Question 1: The 'this' Keyword

The this keyword refers to the object in the current execution context. Typically, within a function, this points to the caller of that function.

Example Question: What will the following code output and why?

const obj = {

name: 'obj',

getName: function() {

return function() {

return this.name;

}

}

}

const fn = obj.getName();

fn();

Answer: The output is undefined.

Analysis: The inner function of getName is executed in the global context, meaning this references the global object, which does not have a name property, resulting in undefined. To ensure that this within the inner function points to obj, you can utilize an arrow function or use the bind method:

const obj = {

name: 'obj',

getName: function() {

return () => {

return this.name;

}

}

}

Question 2: Closures in Action

Question: Create a counter factory function.

function createCounter() {

let count = 0;

return function() {

return count++;

}

}

const counter1 = createCounter();

const counter2 = createCounter();

console.log(counter1()); // 0

console.log(counter1()); // 1

console.log(counter2()); // 0

Analysis: Each counter can increment independently due to the closure created by createCounter, allowing counter1 and counter2 to maintain their own count variables.

Question 3: Event Loop Mechanism

Question: Describe how the event loop works.

Answer: The event loop operates by executing synchronous tasks on the main thread, forming an execution context stack. Once all synchronous tasks are completed, it processes asynchronous tasks from a queue, such as callbacks from Promise.then(), setTimeout, and AJAX requests. The event loop alternates between executing tasks in the stack and processing tasks in the queue, optimizing CPU resource usage.

Question 4: Understanding Promises

Problem: Create a simplified version of a Promise.

The Promise object is a solution for managing asynchronous operations. It can be in one of three states: pending, fulfilled, or rejected.

Implementation Example:

class MyPromise {

constructor(executor) {

this._state = "pending";

this._value = undefined;

this._reason = undefined;

this._onFulfilledCallbacks = [];

this._onRejectedCallbacks = [];

executor(this.resolve.bind(this), this.reject.bind(this));

}

// ... Additional methods here

}

Analysis: The MyPromise class allows you to manage asynchronous tasks effectively, handling various states and providing methods for chaining.

Question 5: Class Inheritance in JavaScript

Question: Implement a People class that inherits from a Person class.

class Person {

constructor(name) {

this.name = name;

}

sayHi() {

console.log(Hello ${this.name})

}

}

class People extends Person {

constructor(name) {

super(name);

}

method() {

console.log('people method')

}

}

const people = new People('John');

people.sayHi(); // Hello John

people.method(); // people method

Analysis: The super keyword allows for inheritance, and method sharing is enabled through the prototype chain.

Question 6: MVC vs. MVVM Patterns

Question: Compare and contrast MVC and MVVM.

In the MVC pattern:

• Model manages data and logic.
• View displays the interface.
• Controller connects the Model and View.

In the MVVM model:

• Model still manages data.
• View displays the interface.
• ViewModel serves as a mediator, facilitating interaction between the Model and View.

Differences:

• MVVM eliminates the Controller, allowing direct binding between View and ViewModel, enabling two-way data synchronization.

The first video titled "Advanced JavaScript Interview Questions" dives deeper into these concepts, providing further insights and examples.

Question 7: AJAX Implementation

Question: Write a function for making AJAX requests.

function ajax(url, options) {

return new Promise((resolve, reject) => {

const xhr = new XMLHttpRequest();

const method = options.method || 'GET';

// Configuration and execution...

});

}

Analysis: This function effectively wraps asynchronous AJAX requests in a Promise, allowing for cleaner handling of asynchronous code.

The second video "Top 10 JavaScript Coding Interview Question and Answers" is essential viewing for anyone preparing for their next interview.

Question 8: JSONP for Cross-Domain Requests

Question: Implement a JSONP request function.

function jsonp(url, options) {

return new Promise((resolve, reject) => {

// Implementation details...

});

}

Analysis: The JSONP function allows for cross-domain requests, leveraging script tags and callback functions.

Question 9: Deep Cloning Objects

Question: Create a deep clone function for objects.

function deepClone(source, clonedMap) {

// Implementation details...

}

Analysis: This function allows for recursive cloning of objects, handling both basic and reference types appropriately.

Question 10: Implementing Function Currying

Question: Write an add function that can handle currying.

function add() {

// Implementation details...

}

Analysis: This function utilizes closures to gather arguments over multiple calls, returning the sum when executed.

Question 11: Custom Promise.all Function

Question: Create a myAll function similar to Promise.all.

function myAll(promises) {

return new Promise((resolve, reject) => {

// Implementation details...

});

}

Analysis: This function aggregates multiple Promises, resolving when all have completed.

Question 12: Implementing the instanceof Operator

Question: Create a function that mimics the behavior of the instanceof operator.

function instanceof(left, right) {

// Implementation details...

}

Analysis: This function checks the prototype chain, determining if one object is an instance of another.

Question 13: Debouncing Function Implementation

Question: Implement a debounce function.

function debounce(fn, delay = 500) {

// Implementation details...

}

Analysis: The debounce function helps control the rate of function execution, particularly useful in handling user input events.

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