# TSR0902: '…' may have changed since it was narrowed: it is assigned in a closure, and '…' on line … can run that closure.

> A local variable that a closure assigns was narrowed, then a call that can run the closure came before its use. Copy it to a const first.

## What it means

A narrowing of a local `let`, `var` or parameter that is assigned inside another function or class body is dropped at every call, `await` and `yield`, because that call can run the closure. Locals never assigned from a closure keep TypeScript's behaviour.

## Example

```ts
// A let assigned inside a closure can change when the closure runs.
function run(): number {
  let cur: string | null = Math.random() > 0.5 ? "a" : null;
  const reset = (): void => {
    cur = null;
  };
  if (cur !== null) {
    reset();
    return cur.length; // @expect TSR0902
  }
  return 0;
}
export const n: number = run();
```

## How to fix

- Copy the variable to a `const` before the call and use the copy.
- Or restructure so the closure doesn't assign the variable.

Sound mode is defined in [design record 0007](https://github.com/Webb-Ventures/typescript-rust/blob/main/docs/design/0007-sound-mode.md) (accepted 2026-10-15).

Source: https://ts-r.dev/errors/TSR0902/