The “TypeError: Cannot read properties of undefined (reading ‘map’)” error occurs when you’re trying to call the `map()` function on an undefined value. This usually happens when your code assumes that a certain variable or property exists, but it doesn’t. In the context of React-JS, this error often occurs when working with arrays or objects that are not properly defined or initialized. Before we dive into the solutions, let’s take a look at some common scenarios that can trigger the “TypeError: Cannot read properties of undefined (reading ‘map’)” error: Using `map()` on an undefined array or object: const arr = undefined; arr.map(item => console.log(item)); Trying to access a non-existent property in an object: const obj = { foo: 'bar' }; obj.nonExistentProperty.map(item => console.log(item)); Using `map()` on an array that’s still being fetched or initialized: const [data, setData] = useState([]); data.map(item => console.log(item)); By MiucciaPosted on July 20, 2024 console.log(item)); console.log(item)); // No error! } else { console.log(‘No data available!’); }