unicodeBOMs

Reports files with Unicode Byte Order Marks (BOMs).

✅ This rule is included in the ts stylistic and stylisticStrict presets.

The Unicode Byte Order Mark (BOM) is a special character (U+FEFF) that can appear at the start of a file to indicate its byte order and encoding. While it can be useful in some contexts, it is generally unnecessary in UTF-8 files and can cause issues with some tools and editors that do not expect it.

Examples

❌ Incorrect

// File starts with BOM character (U+FEFF)
const value = 42;

✅ Correct

// File without BOM character
const value = 42;

Options

This rule is not configurable.

When Not To Use It

If you are working in an environment that specifically requires UTF-8 files to have a BOM, you might choose to disable this rule. However, this is uncommon in modern development, as most tools and editors handle UTF-8 files without a BOM correctly.

Further Reading

• MDN: Byte Order Mark
• Wikipedia: Byte Order Mark
• UTF-8 and Unicode FAQ

Equivalents in Other Linters

• ESLint: unicode-bom
• Oxlint: eslint/unicode-bom