Promises vs Callbacks in JavaScript: Improving Async Code

JavaScript Interview Question: What is Promise.race()? Answer: Promise.race() returns the result of the first promise that settles (resolved or rejected). Example: 𝘗𝘳𝘰𝘮𝘪𝘴𝘦.𝘳𝘢𝘤𝘦([𝘢𝘱𝘪𝘊𝘢𝘭𝘭(), 𝘵𝘪𝘮𝘦𝘰𝘶𝘵()]) Explanation: It is useful when implementing timeouts for API requests. Follow-up Interview Question: What happens if the first Promise rejects? Answer: The entire Promise.race() rejects immediately. #javascript #promises #AsyncProgramming #SoftwareEngineering

JavaScript Interview Question: What is Promise.allSettled()? Answer: Promise.allSettled() waits for all promises to finish regardless of success or failure. Example: 𝘗𝘳𝘰𝘮𝘪𝘴𝘦.𝘢𝘭𝘭𝘚𝘦𝘵𝘵𝘭𝘦𝘥([𝘱𝘳𝘰𝘮𝘪𝘴𝘦1, 𝘱𝘳𝘰𝘮𝘪𝘴𝘦2]) Explanation: It returns an array of objects describing each promise result. Follow-up Interview Question: When should you use Promise.allSettled() instead of Promise.all()? Answer: When you need results from all promises even if some fail. #javascript #promises #AsyncProgramming #WebDevelopment

JavaScript Interview Question: What is the difference between async/await and Promises? Answer: async/await is syntax built on top of Promises that allows writing asynchronous code in a synchronous style. Example: 𝘤𝘰𝘯𝘴𝘵 𝘥𝘢𝘵𝘢 = 𝘢𝘸𝘢𝘪𝘵 𝘧𝘦𝘵𝘤𝘩("/𝘢𝘱𝘪") Explanation: async/await improves readability and reduces nested .then() chains. Follow-up Interview Question: Does async/await remove Promises internally? Answer: No. Explanation: async/await still uses Promises under the hood. #javascript #AsyncProgramming #WebDevelopment #SoftwareEngineering

JavaScript Interview Question: What is Promise.all()? Answer: Promise.all() runs multiple promises in parallel and resolves when all succeed. Example: 𝘗𝘳𝘰𝘮𝘪𝘴𝘦.𝘢𝘭𝘭([𝘧𝘦𝘵𝘤𝘩𝘜𝘴𝘦𝘳𝘴(), 𝘧𝘦𝘵𝘤𝘩𝘗𝘰𝘴𝘵𝘴()])  .𝘵𝘩𝘦𝘯(([𝘶𝘴𝘦𝘳𝘴, 𝘱𝘰𝘴𝘵𝘴]) => {   𝘤𝘰𝘯𝘴𝘰𝘭𝘦.𝘭𝘰𝘨(𝘶𝘴𝘦𝘳𝘴, 𝘱𝘰𝘴𝘵𝘴)  }) Explanation: If any Promise fails, Promise.all() immediately rejects. Follow-up Interview Question: When should you use Promise.all()? Answer: When multiple independent async tasks can run simultaneously. #javascript #promises #AsyncProgramming #FrontendDevelopment

JavaScript Interview Question: What is a Promise in JavaScript? Answer: A Promise is an object that represents the eventual completion or failure of an asynchronous operation. A Promise can be in three states: 1. pending 2. fulfilled 3. rejected Example: 𝘤𝘰𝘯𝘴𝘵 𝘱𝘳𝘰𝘮𝘪𝘴𝘦 = 𝘯𝘦𝘸 𝘗𝘳𝘰𝘮𝘪𝘴𝘦((𝘳𝘦𝘴𝘰𝘭𝘷𝘦, 𝘳𝘦𝘫𝘦𝘤𝘵) => {  𝘴𝘦𝘵𝘛𝘪𝘮𝘦𝘰𝘶𝘵(() => 𝘳𝘦𝘴𝘰𝘭𝘷𝘦("𝘋𝘰𝘯𝘦"), 1000) }) Explanation: Promises allow developers to handle asynchronous operations without deeply nested callbacks. They make async code easier to read and manage. Follow-up Interview Question: Why were Promises introduced in JavaScript? Answer: To solve problems like callback hell and better manage asynchronous workflows. #javascript #promises #AsyncProgramming #WebDevelopment

🚀 Day 23/100 – #100DaysOfCode JavaScript Interview Questions (Advanced Concepts) Continuing with JavaScript fundamentals, today I reviewed some important interview questions that test a deeper understanding of how JavaScript works under the hood. 🔹 Hoisting Hoisting is JavaScript’s behavior where variable and function declarations are moved to the top of their scope before execution. var is hoisted with undefined, while let and const are hoisted but remain in the temporal dead zone. 🔹 Callback Function A callback is a function passed as an argument to another function, which is executed later. Commonly used in: -Asynchronous operations (API calls) -Event handling 🔹 Closure A closure is a function that remembers variables from its lexical scope even after the outer function has finished execution. This is heavily used in: -Data encapsulation -Maintaining private variables 🔹 Pass by Value vs Pass by Reference Pass by Value: A copy of the value is passed (Primitive types) Pass by Reference: A reference to the original object is passed (Objects, Arrays) Changes in reference types affect the original data, while primitive changes do not. Understanding these concepts is critical because they often separate beginners from intermediate developers in interviews. 23 days down, 77 more to go. #Day23 #100DaysOfCode #JavaScript #FrontendDevelopment #WebDevelopment #CodingInterview #MERN

JavaScript Interview Question: What are the states of a Promise? Answer: A Promise has three states: 1. Pending → initial state 2. Fulfilled → operation completed successfully 3. Rejected → operation failed Example: 𝘧𝘦𝘵𝘤𝘩("/𝘢𝘱𝘪")  .𝘵𝘩𝘦𝘯(𝘳𝘦𝘴 => 𝘳𝘦𝘴.𝘫𝘴𝘰𝘯())  .𝘤𝘢𝘵𝘤𝘩(𝘦𝘳𝘳 => 𝘤𝘰𝘯𝘴𝘰𝘭𝘦.𝘦𝘳𝘳𝘰𝘳(𝘦𝘳𝘳)) Explanation: Once a Promise is fulfilled or rejected, its state becomes immutable and cannot change. Follow-up Interview Question: Can a Promise change state after it is fulfilled? Answer: No. Explanation: Once resolved or rejected, a Promise cannot transition to another state. #javascript #promises #AsyncProgramming #SoftwareEngineering

5 Advanced JavaScript Interview Questions Every Developer Should Know 🚀 JavaScript interviews often go beyond the basics. Understanding core concepts helps you write cleaner, scalable, and more efficient code. Here are 5 important JavaScript questions every developer should know: 1️⃣ What are Closures in JavaScript? A closure occurs when a function remembers variables from its outer scope, even after the outer function has finished executing. 2️⃣ What is the Event Loop? The Event Loop allows JavaScript to handle asynchronous operations (API calls, timers, promises) by managing the call stack and callback queue. 3️⃣ Difference between == and ===? • == → Compares values after type conversion • === → Strict comparison (value + type) 4️⃣ What is Hoisting? Hoisting means variable and function declarations are moved to the top of their scope during the compilation phase. 5️⃣ What are Promises? Promises are used to handle asynchronous operations and have three states: Pending → Fulfilled → Rejected 💡 Mastering these concepts helps developers build scalable and reliable applications. #JavaScript #WebDevelopment #Frontend #Programming #CodingInterview #Developers

💡 this Keyword in JavaScript 🧠 What is this? this refers to the object that is currently executing the function. ⚡ Why is it tricky? The value of this changes depending on how a function is called. 🧠 Think Like This Function call → this = global / undefined Object method → this = that object Arrow function → this = inherited from parent 🎯 Interview One-Liner this depends on the calling context of the function. 📌 Used In Object methods Class components Event handlers #JavaScript #ThisKeyword #FrontendDevelopment #InterviewTips #WebDevelopment

💡 JavaScript Technical Interview Prep: What is Currying, and how do you implement it? The Answer: Currying is a functional programming technique that transforms a function expecting multiple arguments into a sequence of nested functions, each taking exactly one argument at a time. Instead of calling a function like sum(1, 2, 3), a curried version allows you to call it as sum(1)(2)(3). - Why is this useful? 1) Enhanced Reusability: It allows you to break down complex functions into smaller, more modular pieces. 2) Partial Application: You can pre-fill certain arguments of a function and generate a new, specialized function to reuse later. 3) Immutability: Currying does not mutate the original function; it safely returns a new one. #JavaScript #TechInterview