---
source: crates/biome_js_analyze/tests/spec_tests.rs
expression: invalid.ts
---
# Input
```ts
interface Foo {}
class Foo {}

class Foo2 {}
interface Foo2 {}

function f(){
    interface Foo3 {}
    class Foo3 {}
}

{
    interface Foo4 {}
    class Foo4 {}
}

export {}

```

# Diagnostics
```
invalid.ts:2:7 lint/suspicious/noUnsafeDeclarationMerging ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ! This class is unsafely merged with an interface.
  
    1 │ interface Foo {}
  > 2 │ class Foo {}
      │       ^^^
    3 │ 
    4 │ class Foo2 {}
  
  i The interface is declared here.
  
  > 1 │ interface Foo {}
      │           ^^^
    2 │ class Foo {}
    3 │ 
  
  i The TypeScript compiler doesn't check whether properties defined in the interface are initialized in the class.
  

```

```
invalid.ts:4:7 lint/suspicious/noUnsafeDeclarationMerging ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ! This class is unsafely merged with an interface.
  
    2 │ class Foo {}
    3 │ 
  > 4 │ class Foo2 {}
      │       ^^^^
    5 │ interface Foo2 {}
    6 │ 
  
  i The interface is declared here.
  
    4 │ class Foo2 {}
  > 5 │ interface Foo2 {}
      │           ^^^^
    6 │ 
    7 │ function f(){
  
  i The TypeScript compiler doesn't check whether properties defined in the interface are initialized in the class.
  

```

```
invalid.ts:9:11 lint/suspicious/noUnsafeDeclarationMerging ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ! This class is unsafely merged with an interface.
  
     7 │ function f(){
     8 │     interface Foo3 {}
   > 9 │     class Foo3 {}
       │           ^^^^
    10 │ }
    11 │ 
  
  i The interface is declared here.
  
     7 │ function f(){
   > 8 │     interface Foo3 {}
       │               ^^^^
     9 │     class Foo3 {}
    10 │ }
  
  i The TypeScript compiler doesn't check whether properties defined in the interface are initialized in the class.
  

```

```
invalid.ts:14:11 lint/suspicious/noUnsafeDeclarationMerging ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ! This class is unsafely merged with an interface.
  
    12 │ {
    13 │     interface Foo4 {}
  > 14 │     class Foo4 {}
       │           ^^^^
    15 │ }
    16 │ 
  
  i The interface is declared here.
  
    12 │ {
  > 13 │     interface Foo4 {}
       │               ^^^^
    14 │     class Foo4 {}
    15 │ }
  
  i The TypeScript compiler doesn't check whether properties defined in the interface are initialized in the class.
  

```