docs: standard library (#5274)

docs/standard_library.md

@@ -0,0 +1,58 @@
+# Standard library
+
+Deno provides a set of standard modules that are audited by the core team and
+are guaranteed to work with Deno.
+
+Standard library is available at: https://deno.land/std/
+
+## Versioning and stability
+
+Standard library is not yet stable and therefore it is versioned differently
+than Deno. For latest release consult https://deno.land/std/ or
+https://deno.land/std/version.ts.
+
+We strongly suggest to always use imports with pinned version of standard
+library to avoid unintended changes.
+
+## Troubleshooting
+
+Some of the modules provided in standard library use unstable Deno APIs.
+
+Trying to run such modules without `--unstable` CLI flag ends up with a lot of
+TypeScript errors suggesting that some APIs on `Deno` namespace do not exist:
+
+```typescript
+// main.ts
+import { copy } from "https://deno.land/std@0.50.0/fs/copy.ts";
+
+copy("log.txt", "log-old.txt");
+```
+
+```shell
+$ deno run --allow-read --allow-write main.ts
+Compile file:///dev/deno/main.ts
+Download https://deno.land/std@0.50.0/fs/copy.ts
+Download https://deno.land/std@0.50.0/fs/ensure_dir.ts
+Download https://deno.land/std@0.50.0/fs/_util.ts
+error: TS2339 [ERROR]: Property 'utime' does not exist on type 'typeof Deno'.
+    await Deno.utime(dest, statInfo.atime, statInfo.mtime);
+               ~~~~~
+    at https://deno.land/std@0.50.0/fs/copy.ts:90:16
+
+TS2339 [ERROR]: Property 'utimeSync' does not exist on type 'typeof Deno'.
+    Deno.utimeSync(dest, statInfo.atime, statInfo.mtime);
+         ~~~~~~~~~
+    at https://deno.land/std@0.50.0/fs/copy.ts:101:10
+```
+
+Solution to that problem requires adding `--unstable` flag:
+
+```shell
+$ deno run --allow-read --allow-write --unstable main.ts
+```
+
+To make sure that API producing error is unstable check
+[`lib.deno.unstable.d.ts`](https://github.com/denoland/deno/blob/master/cli/js/lib.deno.unstable.d.ts)
+declaration.
+
+This problem should be fixed in the near future.

docs/toc.json

@@ -31,6 +31,9 @@
       "import_maps": "Import maps"
     }
   },
+  "standard_library": {
+    "name": "Standard library"
+  },
   "testing": {
     "name": "Testing"
   },