Function getPlatformExtension

packages/jest-haste-map/src/lib/getPlatformExtension.ts:11–27

(
  file: string,
  platforms?: Array<string>,
)

// Extract platform extension: index.ios.js -> ios
export default function getPlatformExtension(
  file: string,
  platforms?: Array<string>,
): string | null {
  const last = file.lastIndexOf('.');
  const secondToLast = file.lastIndexOf('.', last - 1);
  if (secondToLast === -1) {
    return null;
  }
  const platform = file.slice(secondToLast + 1, last);
  // If an overriding platform array is passed, check that first

  if (platforms && platforms.includes(platform)) {
    return platform;
  }
  return SUPPORTED_PLATFORM_EXTS.has(platform) ? platform : null;
}