objectKeyDuplicates

Reports unnecessary duplicate keys that override previous values.

✅ This rule is included in the ts untyped presets.

Duplicate object keys are legal in JavaScript, but they can lead to unexpected behavior. When duplicate keys exist, only the last value for a given key is used. This can cause confusion and bugs, especially when maintaining the code.

Examples

❌ Incorrect

const object = { a: 1, a: 2 };
Error ts(1117)  ― An object literal cannot have multiple properties with the same name.

const config = {
  port: 3000,
  host: "localhost",
  port: 8080,
Error ts(1117)  ― An object literal cannot have multiple properties with the same name.
};

✅ Correct

const object = { a: 1, b: 2 };

const config = {
  host: "localhost",
  port: 8080,
};

Options

This rule is not configurable.

When Not To Use It

If your project intentionally creates duplicate keys as an unusual style choice, this rule may not be for you. If you have a rare case where duplicate keys are intentional, you can use Flint disable comments for those specific situations instead of completely disabling this rule.

Further Reading

• MDN: Object initializer
• MDN: Working with objects

Equivalents in Other Linters

• Biome: noDuplicateObjectKeys
• ESLint: no-dupe-keys