> ## Documentation Index
> Fetch the complete documentation index at: https://docs.refactron.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Transforms

> The twenty verified transforms shipped in Refactron 0.2 — eleven for Python, nine for TypeScript.

Refactron ships a hand-curated catalog of twenty transforms — eleven for Python, nine for TypeScript. Every transform has been hardened against precondition edge cases, runs through the [three verification gates](/concepts/safety-model), and either commits atomically or skips itself.

You select transforms via the `--transforms` flag (`run --transforms=var_to_const_let,implicit_any`) or the `transforms` array in [`.refactronrc.json`](/configuration/refactronrc). The default is `['all']`.

## Catalog

| Transform ID                        | Language   | What it does                                                             |
| ----------------------------------- | ---------- | ------------------------------------------------------------------------ |
| `callback_to_async_await`           | Python     | Trailing-callback function → `async def` returning the result            |
| `format_to_fstring`                 | Python     | `%`-format and `.format()` calls → f-strings                             |
| `manual_typecheck_to_hints`         | Python     | `isinstance` chain dispatching one parameter → `Union[...]` annotation   |
| `deprecated_api_requests_to_httpx`  | Python     | `requests` imports / calls → `httpx`                                     |
| `class_to_dataclass`                | Python     | Pure `__init__`-assignment classes → `@dataclass`                        |
| `super_no_args`                     | Python     | `super(Class, self).method()` → `super().method()`                       |
| `lru_cache_to_cache`                | Python     | `@lru_cache(maxsize=None)` → `@functools.cache` (≥ 3.9)                  |
| `pep585_generics`                   | Python     | `typing.List/Dict/Tuple/...` → built-in `list`/`dict`/`tuple` (≥ 3.9)    |
| `pep604_optional_union`             | Python     | `Optional[X]` → `X \| None`; `Union[A, B]` → `A \| B` (≥ 3.10)           |
| `datetime_utc_alias`                | Python     | `datetime.timezone.utc` → `datetime.UTC` (≥ 3.11)                        |
| `yield_from_for_loop`               | Python     | `for x in y: yield x` → `yield from y`                                   |
| `var_to_const_let`                  | TypeScript | `var` → `const` (or `let` if reassigned) per binding                     |
| `promise_chains_to_async`           | TypeScript | `.then(...).then(...)` chains → `async`/`await`                          |
| `implicit_any`                      | TypeScript | Add explicit parameter types when all call sites pass the same primitive |
| `commonjs_to_esm`                   | TypeScript | `require` / `module.exports` → ES module `import` / `export`             |
| `promise_constructor_to_async`      | TypeScript | `new Promise((resolve) => resolve(x))` → `async` returning `x`           |
| `indexof_to_includes`               | TypeScript | `arr.indexOf(x) !== -1` → `arr.includes(x)` (ES2016+)                    |
| `object_assign_to_spread`           | TypeScript | `Object.assign({}, a, b)` → `{ ...a, ...b }` (ES2018+)                   |
| `string_concat_to_template_literal` | TypeScript | `"a " + name + "!"` → `` `a ${name}!` `` (ES2015+)                       |
| `vue_set_delete_to_assignment`      | TypeScript | `Vue.set` / `this.$set` → direct assignment; `Vue.delete` → `delete`     |

## Browse the catalog

<CardGroup cols={2}>
  <Card title="callback_to_async_await" icon="python" href="/transforms/callback-to-async-await">
    Python · trailing-callback → `async def`
  </Card>

  <Card title="format_to_fstring" icon="python" href="/transforms/format-to-fstring">
    Python · `%` and `.format()` → f-string
  </Card>

  <Card title="manual_typecheck_to_hints" icon="python" href="/transforms/manual-typecheck-to-hints">
    Python · `isinstance` chain → `Union[...]`
  </Card>

  <Card title="deprecated_api_requests_to_httpx" icon="python" href="/transforms/deprecated-api-requests-to-httpx">
    Python · `requests` → `httpx`
  </Card>

  <Card title="class_to_dataclass" icon="python" href="/transforms/class-to-dataclass">
    Python · plain class → `@dataclass`
  </Card>

  <Card title="super_no_args" icon="python" href="/transforms/super-no-args">
    Python · `super(C, self)` → `super()`
  </Card>

  <Card title="lru_cache_to_cache" icon="python" href="/transforms/lru-cache-to-cache">
    Python · `@lru_cache(maxsize=None)` → `@cache` (≥ 3.9)
  </Card>

  <Card title="pep585_generics" icon="python" href="/transforms/pep585-generics">
    Python · `typing.List/Dict` → `list`/`dict` (PEP 585)
  </Card>

  <Card title="pep604_optional_union" icon="python" href="/transforms/pep604-optional-union">
    Python · `Optional[X]` → `X | None` (PEP 604)
  </Card>

  <Card title="datetime_utc_alias" icon="python" href="/transforms/datetime-utc-alias">
    Python · `datetime.timezone.utc` → `datetime.UTC` (≥ 3.11)
  </Card>

  <Card title="yield_from_for_loop" icon="python" href="/transforms/yield-from-for-loop">
    Python · `for x in y: yield x` → `yield from y`
  </Card>

  <Card title="var_to_const_let" icon="js" href="/transforms/var-to-const-let">
    TypeScript · `var` → `const` / `let`
  </Card>

  <Card title="promise_chains_to_async" icon="js" href="/transforms/promise-chains-to-async">
    TypeScript · `.then().then()` → `async`/`await`
  </Card>

  <Card title="implicit_any" icon="js" href="/transforms/implicit-any">
    TypeScript · annotate inferred-primitive parameters
  </Card>

  <Card title="commonjs_to_esm" icon="js" href="/transforms/commonjs-to-esm">
    TypeScript · `require` / `module.exports` → ESM
  </Card>

  <Card title="promise_constructor_to_async" icon="js" href="/transforms/promise-constructor-to-async">
    TypeScript · `new Promise(...)` → `async`
  </Card>

  <Card title="indexof_to_includes" icon="js" href="/transforms/indexof-to-includes">
    TypeScript · `indexOf(x) !== -1` → `includes(x)` (ES2016+)
  </Card>

  <Card title="object_assign_to_spread" icon="js" href="/transforms/object-assign-to-spread">
    TypeScript · `Object.assign({}, …)` → spread literal (ES2018+)
  </Card>

  <Card title="string_concat_to_template_literal" icon="js" href="/transforms/string-concat-to-template-literal">
    TypeScript · `"…" + x` → template literal (ES2015+)
  </Card>

  <Card title="vue_set_delete_to_assignment" icon="js" href="/transforms/vue-set-delete-to-assignment">
    TypeScript · `Vue.set` / `this.$set` → direct assignment
  </Card>
</CardGroup>

<Note>
  Every transform's "after" output passes [Gate 1 (syntax)](/concepts/safety-model#gate-1-syntax) by construction — the refactorer rebuilds the source from a parsed CST/AST. Gates 2 and 3 (imports + tests) are what catch regressions the local rewrite couldn't predict.
</Note>