Function mapWithBrowserField

packages/vite/src/node/plugins/resolve.ts:1123–1139

* given a relative path in pkg dir, * return a relative path in pkg dir, * mapped with the "map" object * * - Returning `undefined` means there is no browser mapping for this id * - Returning `false` means this id is explicitly externalized for browser

(
  relativePathInPkgDir: string,
  map: Record<string, string | false>,
)

 * - Returning `false` means this id is explicitly externalized for browser
 */
function mapWithBrowserField(
  relativePathInPkgDir: string,
  map: Record<string, string | false>,
): string | false | undefined {
  const normalizedPath = path.posix.normalize(relativePathInPkgDir)

  for (const key in map) {
    const normalizedKey = path.posix.normalize(key)
    if (
      normalizedPath === normalizedKey ||
      equalWithoutSuffix(normalizedPath, normalizedKey, '.js') ||
      equalWithoutSuffix(normalizedPath, normalizedKey, '/index.js')
    ) {
      return map[key]
    }
  }
}

function equalWithoutSuffix(path: string, key: string, suffix: string) {
  return key.endsWith(suffix) && key.slice(0, -suffix.length) === path