# TS1138: Parameter declaration expected.

> A parameter list has an empty slot, as in `f(a, , b)`. Remove the extra comma or name the parameter.

## What it means

Each comma in a parameter list must separate two parameter declarations. This is reported
where a parameter should start but doesn't.

## Example

```ts
export function f(a: number, , b: number) {}
```

## How to fix

- Delete the extra comma, or add the missing parameter name.

Source: https://ts-r.dev/errors/TS1138/