React onClick Patterns: Timing and Optimization

Why is your useEffect sitting idle even after you've updated the variable? Look at this snippet. If you’re coming from a Vanilla JS background, count = count + 1 looks perfectly fine. But in React? This code is technically "dead." Why this won't work: * Mutation != Re-render: You are updating a local let variable. React has no "spy" watching your local variables. Unless you call a state setter (like setCount), React doesn't know it needs to re-render the component. * The Lifecycle Gap: useEffect only checks its dependency array ([count]) when the component re-renders. Since the button click doesn't trigger a render, React thinks nothing has changed. * The "Reset" Trap: Even if the component did re-render for some other reason, the first line let count = 0; would run again, resetting your value back to zero every single time. The Fix? Stop treating React like a standard script. Use useState. When you use const [count, setCount] = useState(0), you’re telling React: "Hey, keep an eye on this value. If I change it via setCount, please refresh the UI and check my Effects." Pro-tip: In React, if you want the UI to "react," you have to use the Hook. Simple as that. #ReactJS #WebDevelopment #Frontend #CodingTips #IndiaDevs #Javascript

React fundamentals to get right early Understanding onClick and onChange is key to handling events correctly in React A common pattern to be aware of: onClick={handleClick(id)} This executes immediately during render --- Correct approach: onClick={() => handleClick(id)} This runs only when the user clicks --- Why? React expects a function reference, not a function call - handleClick → correct - handleClick() → executes immediately --- Same concept applies to onChange: onChange={handleChange(value)} // executes immediately Better: onChange={(e) => handleChange(e.target.value)} --- Simple rule: If you need to pass arguments → use an arrow function --- Things to watch out for: - Functions running on every render - Unintended API calls - Difficult-to-debug behavior --- Benefits of correct usage: - Runs only on user interaction - More predictable component behavior - Cleaner and maintainable code --- Additional note: onClick={handleClick} (if your function expects arguments) This may result in "undefined" --- Example: {users.map(user => ( <button onClick={() => handleClick(user.id)}> Click </button> ))} --- Focusing on fundamentals like this helps build more reliable React applications #ReactJS #JavaScript #Frontend #WebDevelopment

A lot of people constantly ask me what React Hooks actually are, and the best way to think about Hooks and JavaScript concepts in general is to look at what problem they were trying to fix. For example, before React Hooks, people would create a Container Component and a Presentational Component. The Container Component would retrieve data, like making a fetch request, and then pass that data down to the Presentational Component, which was usually a pure function that returned some UI, like a div with styling, and accepted that data as props. This pattern helped create a standard for how data was retrieved in React and enforced separation of concerns, but it ended up being too boilerplate heavy for most people. So Hooks were introduced to let us hook into components directly, allowing us to load data as a side effect inside a function while still maintaining separation of concerns without needing extra components. #ReactJs #JavaScript #JavaScriptHooks

Understanding why a component re-renders in React, even when it seems nothing has changed, is crucial for optimizing performance. In the example of the Parent component, we have: ```javascript function Parent() { const [count, setCount] = useState(0); const handleClick = () => { console.log("Clicked"); }; return <Child onClick={handleClick} />; } ``` Even when the Child component is wrapped with React.memo, it still re-renders. The reason is that functions in JavaScript are re-created on every render. Therefore, on each render, `handleClick` is not equal to the previous `handleClick`, leading React to perceive it as a new prop. As a result, the Child component receives a new function reference, prompting React to think the props have changed, which causes the Child to re-render. To prevent this, we can use `useCallback` to memoize the function: ```javascript const handleClick = useCallback(() => { console.log("Clicked"); }, []); ``` This way, React retains the same function reference between renders. Key Insight: React compares references, not function logic. However, it's important to note that `useCallback` should not be overused. It is best utilized when: - Passing functions to child components - Optimizing performance with React.memo #ReactJS #JavaScript #FrontendDevelopment #WebDevelopment #SoftwareEngineering #CodingJourney #LearninglnPublic #DeveloperLife #ReactInternals #FrontendEngineer #TechInterview #StateManagement #ReactHooks

Why do we need to call 'super(props)' in the constructor of a React component? JavaScript classes aren't magic. They are just syntactic sugar over prototypes. If you are still using (or have used) Class Components in React, you have likely typed 'super(props)' a thousand times. But do you actually know what happens if you forget it? In JavaScript, you cannot use the keyword 'this' in a constructor until you have called the parent constructor. Since your component extends 'React.Component', calling 'super()' is what actually initializes the 'this' object. If you try to access 'this.state' or 'this.props' before that call, JavaScript will throw a ReferenceError and crash your app. But why pass 'props' into it? React sets 'this.props' for you automatically after the constructor runs. However, if you want to access 'this.props' inside the constructor itself, you must pass them to 'super(props)'. If you just call 'super()', 'this.props' will be undefined until the constructor finishes execution. Most of us have moved to Functional Components where this isn't an issue. But understanding these fundamentals is what separates a developer who just writes code from one who understands the runtime. #ReactJS #Javascript #SoftwareEngineering #WebDevelopment #Coding #ProgrammingTips

🔥 Stale Closure in React — A Common Bug You Must Know Ever faced a situation where your state is not updating correctly inside setTimeout / setInterval / useEffect? 🤯 👉 That’s called a Stale Closure --- 💡 What is happening? A function captures the old value of state and keeps using it even after updates. --- ❌ Example (Buggy Code): import { useState, useEffect } from "react"; function Counter() { const [count, setCount] = useState(0); useEffect(() => { setInterval(() => { console.log(count); // ❌ Always logs 0 (stale value) }, 1000); }, []); return ( <button onClick={() => setCount(count + 1)}> Count: {count} </button> ); } 👉 Why? Because the closure captured "count = 0" when the effect first ran. --- ✅ Fix (Correct Approach): useEffect(() => { const id = setInterval(() => { setCount(prev => prev + 1); // ✅ always latest value }, 1000); return () => clearInterval(id); }, []); --- 🎯 Key Takeaway: Closures + async code (setTimeout, setInterval, event listeners) = ⚠️ potential stale state bugs --- 💬 Interview One-liner: “Stale closure happens when a function uses outdated state due to how closures capture variables.” --- 🚀 Mastering this concept = fewer bugs + stronger React fundamentals #ReactJS #JavaScript #Frontend #InterviewPrep #Closures #WebDevelopment

Today I learned about the useRef hook in React, and it’s actually very useful! What is useRef? It allows us to create a reference that persists across renders without causing re-renders. Key Uses: Access DOM elements directly Store mutable values without re-rendering Useful for focus, timers, and previous values Example: import { useRef } from "react"; function InputFocus() { const inputRef = useRef(null); const handleClick = () => { inputRef.current.focus(); }; return ( <> <input ref={inputRef} type="text" /> <button onClick={handleClick}>Focus Input</button> </> ); } What I learned: Unlike state, updating useRef does NOT trigger a re-render. Excited to explore more React hooks! #ReactJS #FrontendDevelopment #WebDevelopment #JavaScript #LearningInPublic #90DaysOfCode

Day 19: Custom Hooks in React If you want to write clean, reusable, and professional React code, you must understand Custom Hooks. 📌 What is a Custom Hook? A Custom Hook is a JavaScript function that starts with use and allows you to reuse React logic (state + effects) across multiple components. 👉 Example: useFetch, useAuth, useLocalStorage 📌 Why Custom Hooks are useful? Without custom hooks, we often repeat the same logic again and again ❌ Custom hooks help us: ✅ Reuse logic ✅ Keep components clean ✅ Reduce duplicate code ✅ Improve maintainability 📌 Example: Custom Hook (useCounter) import { useState } from "react"; function useCounter(initialValue = 0) { const [count, setCount] = useState(initialValue); const increase = () => setCount(prev => prev + 1); const decrease = () => setCount(prev => prev - 1); const reset = () => setCount(initialValue); return { count, increase, decrease, reset }; } export default useCounter; 📌 Using the Custom Hook import useCounter from "./useCounter"; function CounterApp() { const { count, increase, decrease, reset } = useCounter(5); return ( <div> <h1>{count}</h1> <button onClick={increase}>+</button> <button onClick={decrease}>-</button> <button onClick={reset}>Reset</button> </div> ); } 📌 Key Point Custom Hooks do not return JSX. They return logic (state + functions). 📌 Real-world Use Cases 🔥 Authentication Hook (useAuth) 🔥 API Fetch Hook (useFetch) 🔥 Theme Hook (useTheme) 🔥 LocalStorage Hook (useLocalStorage) #ReactJS #CustomHooks #FrontendDevelopment #JavaScript #WebDevelopment #LearnInPublic #CodingJourney

𝐓𝐫𝐢𝐜𝐤𝐲 𝐑𝐞𝐚𝐜𝐭 𝐂𝐥𝐨𝐬𝐮𝐫𝐞 𝐈𝐧𝐭𝐞𝐫𝐯𝐢𝐞𝐰 𝐐𝐮𝐞𝐬𝐭𝐢𝐨𝐧 🤔 Many developers understand closures in JavaScript… but get confused when it comes to React. Question: What will be the output of this code? Example 👇 import React, { useState } from "react"; export default function App() { const [count, setCount] = useState(0); const handleClick = () => { setTimeout(() => { console.log(count); }, 1000); }; return ( <> Click </> ); } Now imagine: You click the button 3 times quickly and count updates each time What will be logged after 1 second? Answer 👇 It will log the SAME value multiple times ❌ Why? Because of closure. The setTimeout callback captures the value of count at the time handleClick was created. This is called a “stale closure”. Correct approach ✅ setTimeout(() => { setCount(prev => { console.log(prev); return prev; }); }, 1000); Or use useRef for latest value. Tip for Interview ⚠️ Closures + async code can lead to stale state bugs in React. Good developers know closures. Great developers know how closures behave in React. #ReactJS #JavaScript #Closures #FrontendDeveloper #WebDevelopment #ReactInterview #CodingInterview #ReactHooks

The Virtual DOM is often explained as a "performance optimization." It isn't. Rich Harris made this argument in 2018 and it still stands — VDOM adds a layer of work on top of DOM operations, not below them. What it gives you is a programming model: describe the output, not the steps. I wrote a tutorial that builds the entire engine from scratch in 71 lines of vanilla JS. Four functions. Zero dependencies. Every design decision is explicit — no magic. If you've ever wondered what React's reconciler actually does, this is the fastest path to understanding it. https://lnkd.in/dXvCzgXy #javascript #react #webdev #frontend #tutorial