docs(rustdoc): document that JS/TS checks run under tidy (eslint, es-check, tsc)
diff --git a/src/rustdoc.md b/src/rustdoc.md
index 9290fcd..4181c2f 100644
--- a/src/rustdoc.md
+++ b/src/rustdoc.md
@@ -60,6 +60,18 @@
* Use `./x test tests/rustdoc*` to run the tests using a stage1
rustdoc.
* See [Rustdoc internals] for more information about tests.
+* Use `./x.py test tidy --extra-checks=js` to run rustdoc’s JavaScript checks (`eslint`, `es-check`, and `tsc`).
+> **Note:** `./x.py test tidy` already runs these checks automatically when JS/TS sources changed; `--extra-checks=js` forces them explicitly.
+
+### JavaScript CI checks
+
+Rustdoc’s JavaScript and TypeScript are checked during CI by `eslint`, `es-check`, and `tsc` (not by compiletest). These run as part of the `tidy` job.
+
+```bash
+./x.py test tidy --extra-checks=js
+```
+
+The `--extra-checks=js` flag enables the frontend linting that runs in CI.
[`bootstrap.toml`]: ./building/how-to-build-and-run.md
