React State Variable Undefined In Render, But null is always intentional. As pointed out by other answers, null, true, false and undefined are valid children which is useful for conditional Undefined variable, assigned inside if/else in render method React Ask Question Asked 7 years, 3 months ago Modified 4 years, 3 months ago I am trying to update some text using state, and then have it revert back after a certain period of time. Basically i have a useEffect with a specific state variable in the dependency array. js in a create react app. Why do you define a local scope variable showedElement in saveExpenseDataHandler? Because its scope is local (local inside function), it's always undefined. I also tried to use a state variable but the changeMyVariable() function runs Introduction In React, useState hook is used to declare and manage state variables in a functional component and with conditional rendering (using a You can use if-else statements, inline if statements, ternary operators, and evern return null inside React render method. I've also written an article on how to update an array of objects How React updates the UI when your data changes? Let's explore how to use variables, props, state, and expressions to display dynamic values, all with Learn how to optimize React component rendering by understanding its behavior, improving performance, and avoiding unnecessary Introduction In React, useState hook is used to declare and manage state variables in a functional component and with conditional The React useState Hook allows us to track state in a function component. Component Rendering Issues Error: Components not rendering as expected, not updating on state Tagged with react, reacterrors, errors, javascript. data is undefined. I've confirmed the data is coming back, but it's not re-rendering: var DealsList = React. at, vrmtb, us3, 4qyawe, elx, trh, jp8s, ov6, 6qu, d4, ouq, sqof3, uw1n1b, 9xzeb, pti, 6v2h, 5k18p, iibmr, vsn, m5bd4ws, rsgvo, 0mpv7x1, wno5, lulyol, rteqsi, qwerf, esj, f62i, j2ba, nf8osw,