noDuplicateObjectKeys

JSON (and super languages)

Summary

• Rule available since: v1.0.0
• Diagnostic Category: lint/suspicious/noDuplicateObjectKeys
• This rule is recommended, which means is enabled by default.
• This rule doesn’t have a fix.
• The default severity of this rule is error.

How to configure

biome.json

{
  "linter": {
    "rules": {
      "suspicious": {
        "noDuplicateObjectKeys": "error"
      }
    }
  }
}

Description

Disallow two keys with the same name inside objects.

Examples

Invalid

{
  "title": "New title",
  "title": "Second title"
}

code-block.json:2:3 lint/suspicious/noDuplicateObjectKeys ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ The key title was already declared.
  
    1 │ {
  > 2 │   “title”: “New title”,
      │   ^^^^^^^
    3 │   “title”: “Second title”
    4 │ }
  
  ℹ This is where a duplicated key was declared again.
  
    1 │ {
    2 │   “title”: “New title”,
  > 3 │   “title”: “Second title”
      │   ^^^^^^^
    4 │ }
    5 │ 
  
  ℹ If a key is defined multiple times, only the last definition takes effect. Previous definitions are ignored.
  

Valid

{
  "title": "New title",
  "secondTitle": "Second title"
}

Related links

• Disable a rule
• Configure the code fix
• Rule options
• Source Code
• Test Cases

JavaScript (and super languages)

Summary

• Rule available since: v1.0.0
• Diagnostic Category: lint/suspicious/noDuplicateObjectKeys
• This rule is recommended, which means is enabled by default.
• This rule has an unsafe fix.
• The default severity of this rule is error.
• Sources:
  • Same as no-dupe-keys

How to configure

biome.json

{
  "linter": {
    "rules": {
      "suspicious": {
        "noDuplicateObjectKeys": "error"
      }
    }
  }
}

Description

Disallow two keys with the same name inside objects.

If an object property with the same name is defined multiple times (except when combining a getter with a setter), only the last definition makes it into the object and previous definitions are ignored, which is likely a mistake.

Examples

Invalid

const obj = {
     a: 1,
     a: 2,
}

code-block.js:2:5 lint/suspicious/noDuplicateObjectKeys  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This property is later overwritten by an object member with the same name.
  
    1 │ const obj = {
  > 2 │    	a: 1,
      │    	^^^^
    3 │    	a: 2,
    4 │ }
  
  ℹ Overwritten with this property.
  
    1 │ const obj = {
    2 │    	a: 1,
  > 3 │    	a: 2,
      │    	^^^^
    4 │ }
    5 │ 
  
  ℹ If an object property with the same name is defined multiple times (except when combining a getter with a setter), only the last definition makes it into the object and previous definitions are ignored.
  
  ℹ Unsafe fix: Remove this property.
  
    1 1 │   const obj = {
    2   │ - ···→ a:·1,
    3 2 │      	a: 2,
    4 3 │   }
  

const obj = {
     set a(v) {},
     a: 2,
}

code-block.js:2:5 lint/suspicious/noDuplicateObjectKeys  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This setter is later overwritten by an object member with the same name.
  
    1 │ const obj = {
  > 2 │    	set a(v) {},
      │    	^^^^^^^^^^^
    3 │    	a: 2,
    4 │ }
  
  ℹ Overwritten with this property.
  
    1 │ const obj = {
    2 │    	set a(v) {},
  > 3 │    	a: 2,
      │    	^^^^
    4 │ }
    5 │ 
  
  ℹ If an object property with the same name is defined multiple times (except when combining a getter with a setter), only the last definition makes it into the object and previous definitions are ignored.
  
  ℹ Unsafe fix: Remove this setter.
  
    1 1 │   const obj = {
    2   │ - ···→ set·a(v)·{},
    3 2 │      	a: 2,
    4 3 │   }
  

Valid

const obj = {
     a: 1,
     b: 2,
}

const obj = {
     get a() { return 1; },
     set a(v) {},
}

Related links

• Disable a rule
• Configure the code fix
• Rule options
• Source Code
• Test Cases