---
source: crates/biome_js_analyze/tests/spec_tests.rs
expression: invalidClass.ts
---
# Input
```ts
class D {
	f(a: D): D | undefined { return; }
}

export {}
```

# Diagnostics
```
invalidClass.ts:1:7 lint/correctness/noUnusedVariables ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ! This class is unused.
  
  > 1 │ class D {
      │       ^
    2 │ 	f(a: D): D | undefined { return; }
    3 │ }
  
  i Unused variables usually are result of incomplete refactoring, typos and other source of bugs.
  

```

```
invalidClass.ts:2:4 lint/correctness/noUnusedVariables  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ! This parameter is unused.
  
    1 │ class D {
  > 2 │ 	f(a: D): D | undefined { return; }
      │ 	  ^
    3 │ }
    4 │ 
  
  i Unused variables usually are result of incomplete refactoring, typos and other source of bugs.
  
  i Unsafe fix: If this is intentional, prepend a with an underscore.
  
    1 1 │   class D {
    2   │ - → f(a:·D):·D·|·undefined·{·return;·}
      2 │ + → f(_a:·D):·D·|·undefined·{·return;·}
    3 3 │   }
    4 4 │   
  

```