Mastering useEffect in React: A Simple Guide

🚀 Understanding useEffect in React — Simplified! If you're working with React, mastering useEffect is not optional— 👉 It controls how your app interacts with the outside world. 💡 What is useEffect? useEffect is a hook that lets you perform side effects in components. 👉 Side effects include: API calls Event listeners Timers DOM updates ⚙️ Basic Syntax useEffect(() => { // side effect logic }, [dependencies]); 🧠 How it works 1️⃣ Runs after component renders 2️⃣ Re-runs when dependencies change 3️⃣ Cleanup runs before next effect or unmount 🔹 Example useEffect(() => { console.log("Component mounted or updated"); }, []); 👉 Runs only once (on mount) 🔹 With Dependency useEffect(() => { console.log("Count changed"); }, [count]); 👉 Runs when count changes 🔹 Cleanup Function useEffect(() => { const timer = setInterval(() => { console.log("Running..."); }, 1000); return () => clearInterval(timer); }, []); 👉 Prevents memory leaks 🧩 Real-world use cases ✔ Fetching API data ✔ Subscribing to events ✔ Setting intervals / timeouts ✔ Syncing with external systems 🔥 Best Practices (Most developers miss this!) ✅ Always use dependency array correctly ✅ Cleanup side effects properly ✅ Split multiple effects into separate useEffects ❌ Don’t ignore dependencies (can cause bugs) ❌ Don’t overuse useEffect unnecessarily ⚠️ Common Mistake useEffect(() => { fetchData(); }, []); 👉 If fetchData depends on props/state → can cause bugs 💬 Pro Insight useEffect is not just about running code— 👉 It’s about syncing your component with external systems 📌 Save this post & follow for more deep frontend insights! 📅 Day 13/100 #ReactJS #FrontendDevelopment #JavaScript #ReactHooks #useEffect #WebDevelopment #SoftwareEngineering #100DaysOfCode 🚀

🧠 React Doesn’t Update State Immediately (Even Inside the Same Function) Most people know state is async. But here’s the part many don’t realize 👇 Example const [count, setCount] = useState(0); function handleClick() { setCount(count + 1); if (count === 0) { console.log("Still zero?"); } } You click the button. Expected: count = 1 But inside that function… 👉 count is still 0 🔍 Why? Because React doesn’t update state inside the current render cycle. It schedules the update and re-renders later. 🧠 The tricky part Even this won’t work: setCount(count + 1); setCount(count + 1); 👉 Final result = +1, not +2 ✅ Correct way setCount(prev => prev + 1); setCount(prev => prev + 1); Now React uses the latest value. 🎯 The Real Insight State inside a function is a snapshot, not a live value. 💥 Why this matters This causes: Unexpected conditions Wrong calculations Confusing bugs #ReactJS #FrontendDevelopment #JavaScript #ReactHooks #WebDevelopment #CodingTips #LearningInPublic

🚀 Understanding `useState` & `useEffect` in React If you're working with React, these two hooks are must-know fundamentals: 🔹 **useState** * Used to create and manage state inside a functional component * Returns a state value and a setter function * Triggers re-render when state changes Example: ```js const [count, setCount] = useState(0); ``` 🔹 **useEffect** * Used for side effects (API calls, subscriptions, DOM updates) * Runs after the component renders * Can depend on state or props Example: ```js useEffect(() => { console.log("Component mounted or count changed"); }, [count]); ``` 💡 **Why `useState` should be declared before `useEffect`?** React hooks follow a strict rule: 👉 Hooks must be called in the same order on every render. Since `useEffect` often depends on state values, defining `useState` first ensures: * State is initialized before being used * Dependencies inside `useEffect` are available * Hook order remains consistent (avoiding bugs or crashes) ⚠️ Breaking hook order can lead to unexpected behavior and hard-to-debug issues. ✅ Always follow: 1. Declare state (`useState`) 2. Then handle side effects (`useEffect`) --- Mastering these basics makes your React apps more predictable and maintainable 💻✨ #React #JavaScript #WebDevelopment #Frontend #Programming #ReactHooks

Day 26 #100DaysOfCode 💻 Today I learned about Function, Component, State & Event in Next.js. 🔹 Function Functions are reusable blocks of code used to perform specific tasks. 🔹 Component In Next.js, everything is a component. It helps to break UI into reusable pieces. 🔹 State State is used to store dynamic data inside a component and re-render UI when data changes. 🔹 Event Events handle user interactions like clicks, input, form submission, etc. 💻 Code Snippet: "use client"; import { useState } from "react"; export default function Counter() { const [count, setCount] = useState(0); const handleClick = () => { setCount(count + 1); }; return ( <div> <h2>Count: {count}</h2> <button onClick={handleClick}>Increase</button> </div> ); } 🚀 Small reflection: Understanding these core concepts makes building dynamic and interactive apps much easier. #NextJS #ReactJS #WebDevelopment #JavaScript #Frontend #CodingJourney #Akbiplob

Most React devs know when to use useLayoutEffect. Almost none can explain why it behaves differently. The answer lives inside the commit phase. React's update cycle has two big stages: render (reconcile, diff, no DOM writes) and commit (apply changes, run effects). Commit itself splits into 3 sub-phases: → Before Mutation — read DOM snapshots before anything changes → Mutation — insert, update, remove DOM nodes → Layout — refs attached, useLayoutEffect fires here, synchronously useEffect never runs in the Layout pass. During reconciliation, React builds an Effect List — fiber nodes tagged with pending work. Fibers marked HookLayout flush during the Layout sub-phase. Fibers marked HookPassive get handed to the scheduler and run after the browser paints. React docs put it directly: "React guarantees that the code inside useLayoutEffect and any state updates scheduled inside it will be processed before the browser repaints the screen." Classic case where this matters: tooltip positioning. With useEffect, users catch a flicker — the tooltip renders in the wrong spot, then jumps. With useLayoutEffect, both renders complete before any pixel changes on screen. The tradeoff: useLayoutEffect blocks paint. Use it only when you need to measure or mutate the DOM before the user sees the frame. Data fetching, subscriptions, analytics — those belong in useEffect. One gotcha: useLayoutEffect is a no-op in SSR. React will warn you. Guard with typeof window !== 'undefined' or default to useEffect in universal code. #frontend #reactjs #javascript #typescript #frontenddevelopment #softwareengineering #webdevelopment

One of the biggest mistakes I made early in React: 👉 Overusing useEffect. After working with React for 3 years, I realized: Most useEffect usage is unnecessary. Here’s when you should NOT use useEffect 👇 ❌ 1. Deriving state from props If you can calculate it directly during render, don’t store it in state. Bad: const [fullName, setFullName] = useState("") useEffect(() => { setFullName(firstName + " " + lastName) }, [firstName, lastName]) Better: const fullName = firstName + " " + lastName ❌ 2. Handling simple calculations React re-renders already — no need for effects. ❌ 3. Updating state based on another state This often leads to unnecessary re-renders or bugs. ✅ When should you use useEffect? API calls Subscriptions (e.g., WebSocket) DOM side effects 💡 Rule I follow now: “If it can be calculated during render, don’t use useEffect.” This one shift made my code: ✔ Simpler ✔ Easier to debug ✔ More performant React is powerful — but only when used correctly. What’s one mistake you used to make in React? #React #FrontendDevelopment #JavaScript #CleanCode #WebDev

There's a page in the React docs called "You Might Not Need an Effect." I'd say it's one of the most important pages in the entire React documentation. And most developers have either never read it or read it once and moved on. The whole idea comes down to one question: is your code syncing React with something React doesn't control? A WebSocket, a browser API, a third-party library? If yes, useEffect makes sense. If no, you're probably just adding extra renders and making your code harder to follow. Some patterns worth knowing: If you're deriving a value from props or state, just calculate it during render. No state, no effect needed. If you're responding to a user action like a click or form submit, put it in the event handler. The event handler already knows what happened. The effect doesn't. If you need to reset state when a prop changes, use the key prop. React will remount the component and reset everything automatically. If you're chaining effects where one sets state and triggers another, collapse all of it into a single event handler. React batches those updates into one render. If a child is fetching data just to pass it up to a parent, flip the flow. Let the parent fetch and pass it down. The rule the docs give is honestly the clearest way I've seen it put: if something runs because the user did something, it belongs in an event handler. If it runs because the component appeared on screen, it belongs in an effect. Every unnecessary useEffect is an extra render pass, an extra place for bugs to hide, and more code for the next person to untangle. Worth a read if you haven't: https://lnkd.in/gqUr7e_S How many effects in your current codebase do you think would actually pass that test? #ReactJS #Frontend #JavaScript #WebDevelopment #CleanCode

🧵 Most React devs use useState and useEffect every day — but have no idea what actually happens between setState() and the browser painting the screen. Yes, I know this is a common topic — but I've never seen it explained visually end-to-end in one place. I spent time going deep into the famous React Fiber architecture doc (12.8k stars on GitHub) and broke it all down into one simple carousel. Here's the full React Core pipeline — explained visually 👇 What's inside: ⚡ Why old React used to freeze the browser 🌳 What Virtual DOM actually is (hint: just plain JS objects) 🧵 How Fiber became React's custom call stack 🔍 How the Reconciler diffs trees to find changes ✅ Why the Commit phase can never be interrupted The #1 confusion I see: People think Virtual DOM = Fiber. They're completely different things. → Virtual DOM = a lightweight JS description of your UI → Fiber = the engine that processes that description → Reconciler = the diff algorithm living inside Fiber → Commit = the only moment React actually touches the real DOM Once this clicks, Concurrent Mode, Suspense, and useTransition all make sense. If this helped you, save it for your next React Core interview 🔖 Drop a comment — what part of React internals confused you the most? #ReactJS #JavaScript #WebDev #Frontend #ReactFiber #ReactCore #Programming #SoftwareEngineering #100DaysOfCode #DevCommunity

React vs. Redux vs. Redux Toolkit: Which should you use? "Do I need Redux?" is still one of the most common questions in frontend development. State management can be overwhelming, but understanding the evolution of these tools makes the choice much clearer. Here is a straightforward breakdown of the big three: 1️⃣ React State & Context (The Foundation) React’s built-in hooks (useState, useReducer, useContext) are often all you need. The Good: Zero extra dependencies. It is perfect for local component state (like form inputs or UI toggles) and low-frequency global state (like user themes or auth status). The Bad: Relying purely on Context for high-frequency, complex global state can lead to unnecessary re-renders and messy prop-drilling. 2️⃣ Classic Redux (The Legacy Heavyweight) Redux revolutionized how we handle global state by introducing a single, predictable source of truth. The Good: Unmatched predictability and incredible developer tools (time-travel debugging is magic). The Bad: The boilerplate. Writing separate files for actions, action types, and reducers slows down development and frustrates teams. 3️⃣ Redux Toolkit / RTK (The Modern Standard) Redux Toolkit is not a replacement for Redux; it is the official, modern way to write it. It takes everything great about Redux and strips away the pain points. The Good: It drastically reduces boilerplate. Features like createSlice automatically generate your actions and reducers. It includes Immer under the hood (allowing you to write simpler, "mutating" logic that updates state immutably), and it ships with RTK Query for incredibly efficient data fetching and caching. The Verdict: If you are starting a new project that genuinely needs Redux, RTK is the only way you should be writing it. 💡 My Rule of Thumb: Start simple. Build with React's built-in state. When your state starts feeling tangled, difficult to track, or requires passing props through five layers of components (Prop Drilling)—it's time to bring in Redux Toolkit. How is your team handling state management these days? Are you firmly on team RTK, or have you pivoted to lighter alternatives like Zustand or Jotai? Let's discuss in the comments! 👇 #ReactJS #Redux #WebDevelopment #Frontend #SoftwareEngineering #JavaScript