Write Node.js code that talks to ClickHouse

---
name: clickhouse-js-node-coding
description: >
  Write idiomatic application code with the ClickHouse Node.js client
  (`@clickhouse/client`). Use this skill whenever a user is *building* against
  the Node.js client — configuring the client, pinging, inserting rows in JSON
  or raw formats, selecting and parsing results, binding query parameters,
  managing sessions and temporary tables, working with data types or
  customizing JSON parsing. Do NOT use for browser/Web client code.
---

# ClickHouse Node.js Client — Coding

Reference: https://clickhouse.com/docs/integrations/javascript

> **⚠️ Node.js runtime only.** This skill covers the `@clickhouse/client`
> package running in a **Node.js runtime** exclusively — including **Next.js
> Node runtime** API routes, React Server Components, Server Actions, and
> standard Node.js processes. Do **not** apply this skill to browser client
> components, Web Workers, **Next.js Edge runtime**, Cloudflare Workers, or
> any usage of `@clickhouse/client-web`. For browser/edge environments, the
> correct package is `@clickhouse/client-web`.

---

## How to Use This Skill

1. **Match the user's intent** to a row in the Task Index below and read the
   corresponding reference file before writing code. After reading it, scan any
   **Answer checklist** in that reference and make sure the final answer covers
   each relevant item; those checklists capture details users usually need but
   are easy to omit in short answers.
2. **Always import from `@clickhouse/client`** (never `@clickhouse/client-web`)
   and create a client with `createClient({ url })` or rely on
   supported defaults when appropriate. Close it with `await client.close()`
   preferably when it's no longer needed or during graceful shutdown for global resources.
3. **Prefer `JSONEachRow` for typical row inserts/selects** unless the user
   has already chosen another format or is streaming raw bytes (CSV / TSV /
   Parquet — see `examples/node/performance/`).
   **Note on `clickhouse_settings`:** settings passed to `createClient` are
   defaults for every request; they can be overridden per-call by passing
   `clickhouse_settings` directly to `insert()`, `query()`, or `command()`.
   Always mention this when the user configures settings at the client level.
4. **Always use `query_params` for user-supplied values** — never template-
   literal-interpolate them into SQL. See `reference/query-parameters.md`.
   **When answering a parameter-binding question, your response must
   explicitly name template-literal interpolation as a "SQL injection
   risk"** — even when the user only asked about syntax and did not raise
   security. The literal phrase "SQL injection" needs to appear; this is
   the most common mistake from PostgreSQL/MySQL users and the security
   framing is part of the correct answer, not an optional aside.
5. **Pick the right method for the job:**
   - `client.insert()` — write rows.
   - `client.query()` + `resultSet.json()` / `.text()` / `.stream()` — read
     rows that return data.
   - `client.command()` — DDL and other statements that don't return rows
     (`CREATE`, `DROP`, `TRUNCATE`, `ALTER`, `SET` in a session, etc.).
   - `client.exec()` — when you need the raw response stream of an arbitrary
     statement (rare in coding scenarios).
   - `client.ping()` — health check; returns `{ success, error? }`, never
     throws on connection failure.
6. **Note version constraints** when relevant. Examples:
   - `pathname` config option: client `>= 1.0.0`.
   - `BigInt` values in `query_params`: client `>= 1.15.0`.
   - `TupleParam` and JS `Map` in `query_params`: client `>= 1.9.0`.
   - Configurable `json.parse` / `json.stringify`: client `>= 1.14.0`.
   - `Time` / `Time64` data types: ClickHouse server `>= 25.6`.
   - `Dynamic` / `Variant` / new `JSON` types: ClickHouse server `>= 24.1` /
     `24.5` / `24.8` (no longer experimental since `25.3`).

---

## Task Index

Identify the user's task and read the matching reference file.

| Task                                                     | Triggers / symptoms                                                                                        | Reference file                      |
| -------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------- | ----------------------------------- |
| **Configure / connect the client**                       | Building a `createClient` call, URL parameters, `clickhouse_settings`, default format, custom HTTP headers | `reference/client-configuration.md` |
| **Ping the server**                                      | Health checks, readiness probes, "is ClickHouse up?"                                                       | `reference/ping.md`                 |
| **Choose an insert format**                              | "Which format should I use to insert?", JSON vs raw, `JSONEachRow` vs `JSON` vs `JSONObjectEachRow`        | `reference/insert-formats.md`       |
| **Insert into a subset of columns / different database** | `insert({ columns })`, excluding columns, ephemeral columns, cross-DB inserts                              | `reference/insert-columns.md`       |
| **Insert values, expressions, dates, decimals**          | `INSERT … VALUES` with SQL functions, `Date`/`DateTime` from JS, `Decimal` precision, `INSERT … SELECT`    | `reference/insert-values.md`        |
| **Async inserts (server-side batching)**                 | `async_insert=1`, fire-and-forget vs wait-for-ack                                                          | `reference/async-insert.md`         |
| **Select and parse results**                             | `JSONEachRow` reads, `JSON` with metadata, picking a select format                                         | `reference/select-formats.md`       |
| **Parameterize queries**                                 | Binding values, special characters / escaping, "SQL injection?", `{name: Type}` syntax                     | `reference/query-parameters.md`     |
| **Sessions & temporary tables**                          | `session_id`, `CREATE TEMPORARY TABLE`, per-session `SET` commands                                         | `reference/sessions.md`             |
| **Modern data types**                                    | `Dynamic`, `Variant`, `JSON` (object), `Time`, `Time64`                                                    | `reference/data-types.md`           |
| **Custom JSON parse/stringify**                          | Plug in `JSONBig` / `safe-stable-stringify` / a `BigInt`-aware serializer                                  | `reference/custom-json.md`          |

---

## Conventions used in answers

- Always show `import { createClient } from '@clickhouse/client'` (Node, never
  Web).
- Always `await client.close()` at the end of self-contained snippets; in
  long-running services, close on graceful shutdown.
- For inserts, prefer `format: 'JSONEachRow'` and `values: [...]` unless the
  user's scenario requires otherwise.
- For selects, prefer `await (await client.query({...})).json<RowType>()` for
  small / medium result sets; for bigger results suggest streaming.
- When showing parameter binding, use ClickHouse's native `{name: Type}`
  syntax — never `$1`, `?`, or `:name`.
- For DDL inside a cluster or behind a load balancer, set
  `clickhouse_settings: { wait_end_of_query: 1 }` on the `command()` call so
  the server only acknowledges after the change is applied. See
  https://clickhouse.com/docs/en/interfaces/http/#response-buffering.

---

## Out of scope

This skill covers day-to-day coding against `@clickhouse/client` (Node).
The following topics are intentionally **not** covered here:

- **Errors, hangs, type mismatches, proxy pathname surprises, log silence,
  socket hang-ups, `ECONNRESET`** → use the
  `clickhouse-js-node-troubleshooting` skill.
- **Streaming, Parquet, file streams, server-side bulk moves, progress
  streaming, async-insert throughput tuning** — see
  [`examples/node/performance/`](https://github.com/ClickHouse/clickhouse-js/tree/main/examples/node/performance).
- **TLS, RBAC / read-only users, deeper SQL-injection guidance** — see
  [`examples/node/security/`](https://github.com/ClickHouse/clickhouse-js/tree/main/examples/node/security).
- **`CREATE TABLE` patterns, deployment-shaped connection strings,
  replication / sharding choices** — see
  [`examples/node/schema-and-deployments/`](https://github.com/ClickHouse/clickhouse-js/tree/main/examples/node/schema-and-deployments).
- **Browser, Web Worker, Next.js Edge, Cloudflare Workers** — use
  `@clickhouse/client-web` and see
  [`examples/web/`](https://github.com/ClickHouse/clickhouse-js/tree/main/examples/web).

---

## Still Stuck?

- [`examples/node/coding/`](https://github.com/ClickHouse/clickhouse-js/tree/main/examples/node/coding) — the runnable corpus this skill is built on.
- [ClickHouse JS client docs](https://clickhouse.com/docs/integrations/javascript)
- [ClickHouse supported formats](https://clickhouse.com/docs/interfaces/formats)
- [ClickHouse data types](https://clickhouse.com/docs/sql-reference/data-types)