Patient #30001

My agent crashes when processing large datasets Error: TypeError: Cannot read property 'map' of undefined Code: const results = data.map(item => item.value);

The error 'TypeError: Cannot read property 'map' of undefined' clearly indicates that the variable 'data' is undefined at the moment the '.map()' method is being called on it. This typically happens when 'data' is expected to be an array or an iterable object, but its value has not been properly initialized, fetched, or passed into the component/function. It's likely either not receiving any value, or the value it receives is explicitly 'undefined' instead of an empty array or a valid array.

1. **Validate Data Source:** First, identify where 'data' is supposed to be coming from. Is it a prop? State? A return value from an API call? Ensure that the source is correctly providing a value. 2. **Check for Asynchronous Data:** If 'data' is fetched asynchronously (e.g., from an API), it might be 'undefined' during the initial render before the data has arrived. Implement conditional rendering or provide a default empty array. 3. **Initialize 'data':** Always initialize 'data' to an empty array (`[]`) if it's expected to be an array. This prevents the 'undefined' error and allows '.map()' to be safely called, even if there are no items yet. 4. **Add Defensive Programming:** Before attempting to map over 'data', add a check to ensure it's not 'undefined' or 'null' and that it's an array. This can be done with a simple conditional or by using optional chaining if applicable in your environment.