lancedikson_bowser/AGENTS.md

Agents Instructions for Bowser

Architecture

Bowser parses User-Agent strings through a pipeline of four independent parser modules, each exporting an ordered array of descriptors:

• src/parser-browsers.js → src/parser-os.js → src/parser-platforms.js → src/parser-engines.js

src/parser.js (the Parser class) orchestrates these by iterating each descriptor list using Utils.find(), testing via regex arrays or custom test(parser) functions, then calling describe(ua) on the first match. Descriptor order matters — more specific browsers (e.g., Opera, Edge) must come before generic ones (e.g., Chrome, Safari) to avoid false matches.

src/bowser.js is a stateless facade exposing Bowser.getParser(UA) and Bowser.parse(UA). src/constants.js holds bidirectional maps (BROWSER_ALIASES_MAP ↔ BROWSER_MAP) used for satisfies() alias lookups. src/utils.js provides regex helpers (getFirstMatch, getSecondMatch) and version comparison logic.

Also supports User-Agent Client Hints via an optional clientHints parameter on the constructor.

Commands

• Build: npm run build (Webpack + Babel → es5.js, bundled.js)
• Test: npm test (AVA — runs both test/unit/ and test/acceptance/)
• Lint: npm run lint:check / npm run lint:fix

Adding Browser/Bot Support (5 files to touch)

1. src/parser-browsers.js: Add a descriptor with test (regex array) and describe(ua) returning { name, version }. Place it above any generic browser it might conflict with.
2. src/parser-platforms.js: Add a platform descriptor if the new entry is a bot (return { type: PLATFORMS_MAP.bot, vendor }) or needs specific device detection.
3. src/constants.js: Add entries to both BROWSER_ALIASES_MAP (display name → alias) and BROWSER_MAP (alias → display name). Alias convention: lowercase, underscores for spaces/dashes, drop "browser" suffix (e.g., 'UC Browser' → 'uc', 'Opera Coast' → 'opera_coast').
4. test/acceptance/useragentstrings.yml: Add real UA strings under the browser's display name with full spec (browser, os, platform, engine). The acceptance test iterates this YAML and asserts Bowser.parse(ua) deep-equals the spec. The top-level key must match the browser's name field exactly.
5. index.d.ts: Update TypeScript definitions if adding new API surface.

Run npm test to validate — acceptance tests auto-generate from the YAML file.

Descriptor Pattern

Every parser file exports an array of descriptors following this pattern:

{
  test: [/someregex/i],           // array of RegExp, OR:
  // test(parser) { return parser.test(/regex/); },  // function form for complex logic
  describe(ua) {
    return {
      name: 'BrowserName',
      version: Utils.getFirstMatch(/someregex\/(\d+(\.\d+)+)/i, ua),
    };
  },
}

Engine descriptors in src/parser-engines.js may use test(parser) to access parser.getBrowserName() for browser-dependent engine detection (e.g., Edge → Blink vs EdgeHTML).

satisfies() Version DSL

Parser.satisfies(checkTree) accepts a nested object for conditional browser/OS/platform checks. Keys in the check tree are resolved via BROWSER_ALIASES_MAP (so both 'chrome' and 'Chrome' work). Version operators: >, >=, <, <=, =, ~ (loose/prefix match). Values can be a single string or an array of version strings (OR logic).

// Simple browser check
parser.satisfies({ chrome: '>118', firefox: '~100' })

// Nested by OS or platform
parser.satisfies({ windows: { chrome: '>118' }, macos: { safari: '>=15' } })
parser.satisfies({ desktop: { chrome: '>118' }, mobile: { safari: '>=15' } })

Returns true/false if the browser matches, or undefined if the browser isn't mentioned in the tree. The ~ operator does a loose prefix comparison (e.g., ~100 matches 100.x.x).

Code Conventions

• ES6 modules with explicit .js extensions in imports: import Utils from './utils.js'
• Airbnb ESLint base; underscore-prefixed private properties (_ua, _hints)
• Use void (0) instead of undefined for comparisons (legacy convention)
• JSDoc on all public methods with @param, @return, @example
• Browser versions are always strings, never numbers

Testing Details

• Acceptance tests (test/acceptance/test-list-of-ua.js): Loads useragentstrings.yml, tests every UA against both src/bowser.js (ES6) and es5.js (built) — so build before running tests if you changed source.
• Unit tests (test/unit/): Test individual Parser/Bowser/Utils methods. Use new Parser(UA, true) (skipParsing=true) for isolated method testing.
• Test framework: AVA with Babel transpilation via @babel/register.

Branching

• master is the production branch.

Common Pitfalls

• Always check BROWSER_ALIASES_MAP for existing aliases before adding new ones.
• User-Agent strings can be complex; test edge cases thoroughly.
• Remember to update both the alias map and the reverse map in constants.
• Browser versions should be treated as strings, not numbers.
• Keep regex patterns readable with comments explaining their purpose.