👀 Views: 101 💬 Answers: 1 📅 Created: 2025-06-13

typescript generics type-inference

I'm trying to debug After trying multiple solutions online, I still can't figure this out... I'm working with a frustrating TypeScript behavior when trying to implement a utility function that is supposed to process an array of items, but I keep getting the behavior `Property 'map' does not exist on type 'never'`. I'm using TypeScript 4.5 and have defined a generic function like this: ```typescript function processArray<T>(items: T[]): T[] { return items.map(item => { // some processing on item return item; }); } ``` The scenario arises when I invoke this function with an array of a specific type. For instance: ```typescript const numbers: number[] = [1, 2, 3]; const processedNumbers = processArray(numbers); ``` So far, everything seems straightforward, but when I try to call `processArray` with an array of objects: ```typescript const users = [{ name: 'Alice' }, { name: 'Bob' }]; const processedUsers = processArray(users); ``` TypeScript throws the same behavior, stating that `Property 'map' does not exist on type 'never'.` I initially thought it could be related to the inference of the type `T`, but I explicitly provided the types in my function calls. I've also tried adding type annotations directly to the function parameters, like so: ```typescript function processArray<T extends {}>(items: T[]): T[] { return items.map(item => item); } ``` However, that didn't resolve the scenario. It feels like TypeScript is losing track of the type being passed when the input is an array of objects. Can anyone explain why this is happening and how I can fix this type behavior? Is there a better way to ensure my utility function remains type-safe while avoiding these issues? Any help would be appreciated! What am I doing wrong? This is part of a larger REST API I'm building. Any ideas how to fix this?