Understanding JavaScript Promises: States & Types Explained

𝗝𝗮𝘃𝗮𝗦𝗰𝗿𝗶𝗽𝘁 𝗣𝗿𝗼𝗺𝗶𝘀𝗲𝘀 𝗘𝘅𝗽𝗹𝗮𝗶𝗻𝗲𝗱 JavaScript is single-threaded. This means it can only do one thing at a time. You need to fetch data from an API, read a file, or wait for a timer without freezing your app. This is where promises come in. Promises simplify async tasks. They represent a future value. A promise is like a placeholder for a value that is not available yet. - Promises have three states: - Pending: initial state, waiting for the result - Fulfilled: operation succeeded, value available - Rejected: operation failed, error available Promises can be chained to run multiple async tasks sequentially. This makes your code cleaner and easier to read. Promises are better than callbacks. They are easier to read and maintain. They also make error handling easier. You can use promises to fetch data from an API or read a file. They prevent callback hell. - .then() handles success - .catch() handles errors - Can be chained for sequential async operations Promises are the foundation of modern asynchronous JavaScript. Once you master them, you will be ready for async/await syntax and complex async workflows. Source: https://lnkd.in/gyY3cNir

𝗝𝗮𝘃𝗮𝗦𝗰𝗿𝗶𝗽𝘁 𝗣𝗿𝗼𝗺𝗶𝘀𝗲𝘀 𝗘𝘅𝗽𝗹𝗮𝗶𝗻𝗲𝗱 JavaScript is single-threaded, it can only do one thing at a time. You need to fetch data from an API, read a file, or wait for a timer without freezing your app. This is where promises come in. Promises simplify async tasks. - They prevent callback hell - They represent a future value - They make error handling easy A promise can be in three states: - Pending – initial state, waiting for the result - Fulfilled – operation succeeded, value available - Rejected – operation failed, error available Promises can be chained to run multiple async tasks sequentially. - They are cleaner than nested callbacks - They are easier to read and maintain You can handle success with .then() and errors with .catch(). Promises are the foundation of modern asynchronous JavaScript. Mastering promises will help you with async/await syntax, complex async workflows, and clean code. Source: https://lnkd.in/gyY3cNir

🚨 If you don’t understand THIS in JavaScript, you’re silently creating bugs… Every time you copy an object or array, you think you're safe. But you're not. ❌ Because in JavaScript, copying ≠ copying. 👉 One small mistake between shallow copy and deep copy can: Mutate your original data unexpectedly 😵💫 Break your React state ⚛️ Create bugs that take HOURS to debug 🐛 That’s why I created a complete guide on Deep vs Shallow Copy in JavaScript 👇 📚 In this PDF, you’ll learn: The real difference between primitive & reference types Why ...spread sometimes fails you When shallow copy is enough (and when it’s dangerous) Deep copy methods (JSON, structuredClone, custom functions) Real-world use cases in React & Redux Common pitfalls that even experienced devs miss 💡 This is one of those concepts that: Once you truly understand it… your code becomes predictable, clean, and bug-free. If you're working with: ✔️ React state ✔️ APIs ✔️ Complex objects ✔️ Real-world projects Then this is non-negotiable knowledge. 📌 Save this post for later 📌 Comment “COPY” and I’ll share key insights 📌 Follow for more deep-dive JavaScript content Let’s write better JavaScript—one concept at a time. 🚀

“Hello undefined” — ever seen this in JavaScript? 😵 At first, it feels like a bug… but actually, it’s a misunderstanding of this. In JavaScript, this doesn’t depend on where the function is written, it depends on who is calling the function. And that’s exactly where many developers get stuck. To solve this, JavaScript gives us three powerful methods: → call() → apply() → bind() These let you: • Control the context of this • Borrow functions from other objects • Avoid rewriting the same logic again and again Ek hi function… multiple objects ke saath kaam kare — clean and scalable approach. In this blog, I’ve broken everything down with simple examples and clear intuition — no heavy theory, just practical understanding. If this has ever confused you, this will help you finally connect the dots. 🔗https://lnkd.in/gNc2NYQe #javascript #webdevelopment #frontend #100DaysOfCode #learning #developers

𝗧𝗵𝗲 𝗝𝗮𝗳𝗮𝗦𝗰𝗿𝗶𝗽𝘁 𝗘𝘃𝗲𝗻𝘁 𝗟𝗼𝗼𝗽 You've probably heard that JavaScript is single-threaded. But how does it handle multiple tasks at once? JavaScript achieves concurrency by avoiding blocking. It runs on a single thread, which means one call stack and one task at a time. No parallel execution of your JavaScript code. So, how does it handle multiple tasks? JavaScript: - Executes fast tasks immediately - Delegates slow tasks to the runtime (browser or Node.js) - Continues executing other code - Handles results later JavaScript relies on four components: - Executes code one function at a time - Handles timers, network, etc. - Uses background threads internally - Stores completed async tasks From the outside, it looks like multiple tasks are in progress and results come back later. Nothing blocks execution. This creates the illusion of multiple tasks running at once. But internally, it's actually one task at a time. JavaScript itself is single-threaded, but the environment is not. Background threads are used for timers, network requests, and file system (Node.js). You need Web Workers (browser) or Worker Threads (Node.js) to get parallel execution. JavaScript handles multiple tasks without multithreading by delegating slow work to the runtime and continuing execution immediately. Source: https://lnkd.in/guWSNstx

𝗝𝗮 v𝗮𝗦𝗰𝗿𝗶𝗽𝘁 𝗖𝗹𝗼𝘀𝘂𝗿𝗲𝘀 𝗠𝗮𝗱𝗲 𝗘𝗮𝘀𝘆 You want to understand JavaScript closures. Closures are a powerful concept in JavaScript. They help you write clean and modular code. A closure is created when a function remembers variables from its outer scope. This happens even after the outer function has finished executing. You can access variables from outside a function's scope, even later. Here's an example: - A function returns another function. - The returned function remembers variables from the outer function. - You can use the returned function to access these variables. Closures work because of lexical scope in JavaScript. Functions remember where they were created, not where they are executed. This helps with data privacy. You can use closures to: - Hide data - Create private variables - Make function factories - Handle events - Write async code Closures help with data persistence. They enable private variables. This makes your code clean and modular. You can use closures for data privacy. For example, you can create a bank account function that returns methods to deposit and get the balance. The balance is protected and can only be accessed via these methods. Source: https://lnkd.in/gRZkgUBp

Most JavaScript developers think they understand equality… until this happens: {} === {} // false And suddenly… nothing makes sense. Let me show you what’s REALLY happening 👇 In JavaScript, not all data is equal. 👉 Primitives (numbers, strings…) are stored by value 👉 Objects are stored by reference (in memory) So when you compare objects, you're NOT comparing their content… You're comparing their addresses. Now here’s where things get interesting 🔥 JavaScript doesn’t just compare values… It actually transforms them behind the scenes using something called: 👉 Type Coercion Example: "5" - 1 // 4 Why? Because JS silently converts "5" → number. But what about objects? 🤔 const obj = { id: 105 }; +obj // NaN ❌ JavaScript doesn’t know how to convert it. Except… sometimes it DOES 😳 const t1 = new Date(); const t2 = new Date(); t2 - t1 // works ✅ Wait… how did that happen?! This is where things go from “JavaScript” to magic 🧠✨ Behind the scenes, JS uses: 👉 Symbol.toPrimitive A hidden mechanism that tells the engine: “Hey, if you need to convert this object… here’s how to do it.” And here’s the crazy part 👇 You can control it yourself. const user = { [Symbol.toPrimitive](hint) { return 105; } }; +user // 105 ✅ This is called: 👉 Metaprogramming You’re not just writing code… You’re controlling how the language itself behaves. 💡 Why this matters? Because: You avoid weird bugs You understand how JS REALLY works You level up from “writing code” → “engineering behavior” And now you understand why tools like TypeScript exist… 👉 To protect you from all this hidden complexity. 🚀 Final thought: Most developers try to avoid JavaScript quirks… But the best developers? They understand them… and take control. #JavaScript #Frontend #WebDevelopment #Programming #SoftwareEngineering #TypeScript #CleanCode #100DaysOfCode #MERNStack #CodingTips #LearnToCode

𝗧𝗵𝗲 𝗣𝗼𝘄𝗲𝗿 𝗼𝗳 𝗖𝗮𝗹𝗹𝗯𝗮𝗰𝗸𝘀 𝗶𝗻 𝗝𝗮 v𝗮𝗦𝗰𝗿𝗶𝗽𝘁 JavaScript is powerful. It can handle tasks that take time, like API calls or timers. You need a way to manage these tasks. That's where callbacks come in. A callback is a function passed into another function to be executed later. You can store functions in variables, pass them as arguments, and return them from other functions. - You can pass a function as an argument to another function - You can return a function from another function - You can store a function in a variable Callbacks help with asynchronous operations. JavaScript doesn't wait for long tasks to finish. It keeps running other tasks. Callbacks run after a task is complete. They are used in event handling, like when a button is clicked. Callbacks can become messy when nested. This is called "callback hell". It's hard to read, debug, and maintain. To avoid this, you can use other methods like Promises and Async/Await. Callbacks are important in JavaScript. They enable asynchronous behavior and flexible function execution. They power many built-in features. But you should use them wisely to avoid messy code. Source: https://lnkd.in/g3jd_H2S

JavaScript is single-threaded. So no multithreading… right? Not quite. I used to think that too — until I ran into a UI that froze so hard it felt like the browser went into meditation mode. Turns out, JavaScript doesn’t do parallel execution on the main thread… but it absolutely does concurrency differently. Enter: - Web Workers (browser) - Worker Threads (Node.js) This changed how I think about performance. Instead of blocking the UI with heavy work, you can push it into background threads: data processing image manipulation expensive computations and keep the main thread free to do what it’s meant for: smooth UI, fast interactions, responsive apps. Here’s the important part people often miss: Workers don’t share memory by default. They communicate through message passing (postMessage), like separate systems talking over a clean protocol. No shared state chaos. No accidental race conditions. If you do need shared memory, you step into: SharedArrayBuffer + Atomics (powerful, but requires careful setup and headers) And underneath it all: Each worker runs its own event loop — isolated, independent, predictable. So yes — JavaScript is single-threaded. But modern JS apps? They’re quietly multi-core when you design them right. I learned this the hard way after freezing more UIs than I’d like to admit. What about you — still running everything on the main thread, or have you started pushing work off it?

Stop using `new CustomEvent()`. There is a much better way to handle events in JavaScript. 1. The old habit For years, we have used `CustomEvent` to pass data around. It works, but it has flaws. You have to wrap your data inside a detail property. It feels clunky and "unnatural" compared to other objects. 2. The problem with CustomEvent It creates friction in your code: - The syntax is verbose. - You cannot access your data directly (you always need .detail). - It is difficult to type correctly in TypeScript. 3. The modern solution You don't need `CustomEvent` anymore. You can simply create your own class and extend `Event`. It looks like this: class UserLoginEvent extends Event { ... } 4. Why is it better? Subclassing `Event` is the standard way now. It offers clear advantages: - It uses standard JavaScript class syntax. - Your data sits on the event itself, not inside .detail. - It is much easier to define types for your custom events. - It works in all modern browsers. 5. It is time to upgrade If you want cleaner, strictly typed events, try extending the native `Event` class. It makes your code easier to read and maintain. Do you still use `CustomEvent` or have you switched?