ReactiveX/rxjs · error · Error

Unknown mode: ${mode}

Error message

Unknown mode: ${mode}

What it means

Thrown by parseArguments in the @rxjs/migrate CLI when the value passed to --mode is not one of the supported modes. The CLI only accepts 'cold' (RxJS 7-style cold observable semantics) or 'platform' (native Observable platform semantics); any other string aborts argument parsing before migration runs.

Source

Thrown at packages/migrate/src/cli.ts:140

  for (let index = 0; index < argv.length; index++) {
    const argument = argv[index];
    if (!argument) continue;
    switch (argument) {
      case '--source-root':
        options.sourceRoot = requiredValue(argv, ++index, argument);
        break;
      case '--out-dir':
        options.outputRoot = requiredValue(argv, ++index, argument);
        break;
      case '--source-repo':
        options.repository = requiredValue(argv, ++index, argument);
        break;
      case '--source-sha':
        options.sha = requiredValue(argv, ++index, argument);
        break;
      case '--mode': {
        const mode = requiredValue(argv, ++index, argument);
        if (mode !== 'cold' && mode !== 'platform') throw new Error(`Unknown mode: ${mode}`);
        options.mode = mode;
        break;
      }
      case '--framework': {
        const framework = requiredValue(argv, ++index, argument);
        if (framework !== 'preserve' && framework !== 'mocha-chai-vitest') throw new Error(`Unknown framework: ${framework}`);
        options.framework = framework;
        break;
      }
      case '--write':
        options.write = true;
        break;
      case '--help':
      case '-h':
        options.help = true;
        break;
      default:
        if (argument.startsWith('-')) throw new Error(`Unknown option: ${argument}`);

View on GitHub (pinned to 54796b38a5)

Solutions

1. Set --mode to exactly 'cold' or 'platform'
2. Run with --help to list accepted flag values
3. Check for typos or trailing whitespace/shell quoting in the mode value

Example fix

// before
npx @rxjs/migrate --mode hot --source-root src ...
// after
npx @rxjs/migrate --mode platform --source-root src ...

const MODES = new Set(['cold', 'platform']);
if (!MODES.has(mode)) {
  console.error(`--mode must be one of ${[...MODES].join(' | ')}`);
  process.exitCode = 1;
}

const isMigrationMode = (v: string): v is 'cold' | 'platform' => v === 'cold' || v === 'platform';

try { runCli(argv); } catch (e) { console.error((e as Error).message); /* message already lists the offending value */ }

When it happens

Trigger: Running the CLI with an invalid --mode value, e.g. `rxjs-migrate --mode hot ...`, `--mode rxjs8`, or a typo like `--mode platfrom`. Also triggered when the next token after --mode starts with '-' (via requiredValue) or is missing.

Common situations: Assuming mode names from older migration tooling or docs (e.g. 'v8', 'next', 'hot'), copy-pasting commands from an out-of-date migration guide, or shell quoting mistakes that shift the argument position.

Related errors

• Unknown framework: ${framework}
• Unknown option: ${argument}
• Missing required argument${missing.length === 1 ? '' : 's'}:
• --out-dir is required with --write
• ${option} requires a value

AI-assisted analysis of ReactiveX/rxjs@54796b38a5 (2026-08-28). Data as JSON: /api/errors/dfa4dfad1882eb4a. Report an issue: GitHub.