Biome Toolchain

Biome is a high-performance toolchain for web projects designed to maintain project health. It provides:

• Fast Formatter: Supports JavaScript, TypeScript, JSX, JSON, CSS, and GraphQL with ~97% compatibility with Prettier.
• High-performance Linter: Supports JavaScript, TypeScript, JSX, CSS, and GraphQL with over 500 rules (including those from ESLint and typescript-eslint).
• Editor Integration: Designed for interactive use with first-party extensions and excellent LSP support.

Key characteristics:

• No Node.js required: Biome can run without a Node.js runtime.
• Unified Core: Uses a shared foundation for parsing, error reporting, parallel execution, caching, and configuration, combining functionality that previously required separate tools.

While Biome is a separate tool, it respects // eslint-disable-next-line comments in certain contexts, often appearing alongside // prettier-ignore in codebases that use both tools. However, Biome's primary mechanism for ignoring code is its own ignore comments.

function HelloWorld(x) {
  // prettier-ignore
  // eslint-disable-next-line
  (x.a |
    x.b).call(null);
}

Biome supports suppression comments to ignore specific linting or formatting rules.

• Recommended: Use // biome-ignore.
• Deprecated: // rome-ignore is deprecated and should be replaced with the Biome syntax.

// biome-ignore <rule-name>
const x = 1;

Biome supports the ES2024 Explicit Resource Management syntax (using and await using).

Note that in some cases, such as when using escaped identifiers or specific comment placements, Biome's formatting may differ from Prettier. For example, Biome may escape certain characters in identifiers to ensure consistency:

// Biome might transform this:
await using ab = c;
// To this:
await using \u0061b = c;

async function f() {
  await using \u0061b = c;
}

The overrides option allows you to modify the behavior of the formatter, linter, or other tools for specific file patterns using the include key.

Important: When both include and ignore are specified in a configuration, ignore takes precedence over include.

{
  "formatter": {
    "lineWidth": 100
  },
  "overrides": [
    {
      "include": ["generated/**"],
      "formatter": {
        "lineWidth": 160
      },
      "javascript": {
        "formatter": {
          "quoteStyle": "single"
        }
      }
    },
    {
      "include": ["lib/**"],
      "linter": {
        "rules": {
          "suspicious": {
            "noDebugger": "off"
          }
        }
      }
    }
  ]
}

Biome handles comments following continue and break statements within for loops. In certain edge cases involving labels and comments, Biome may reformat the structure to ensure the comment is correctly associated with the statement, sometimes moving the comment to a new line or adjusting the semicolon placement.

label1: for (;;) continue label1; // comment

End-to-end (e2e) tests in Biome are implemented as individual directories within the e2e-tests directory. Each directory represents a unique project configuration using Biome.

To define a test, every directory must contain a shell script named test.sh. The test's success or failure is determined solely by the exit status of this script. The execution environment automatically sets the working directory to the directory containing the test.sh file.

# Example test.sh content
set -eu

cargo run --bin biome -- lint src

The useLiteralKeys rule has been updated (in v1.8.1 and v1.8.2) to avoid conflicts with the formatter's quoteProperties option. The rule now ignores quoted member names that can be unquoted, preventing it from suggesting changes that contradict your formatting configuration.

// The rule no longer reports these as needing changes if they can be unquoted
const x = { "prop": 0 };