# Node

**Kind:** Class

**Source:** [`src/router/reg-exp-router/node.ts`](https://github.com/honojs/hono/blob/main/src/router/reg-exp-router/node.ts#L45)

**Part of:** [Router](subsystem-src-router)

`Node` stores route data for the regular-expression router and builds the regular-expression source used for matching. It accepts route entries through `insert()` and produces a matcher pattern through `buildRegExpStr()`.

## Methods

| Method | Signature | Returns |
|---|---|---|
| `insert` | `insert(tokens: readonly string[], index: number, paramMap: ParamAssocArray, context: Context, isStatic: boolean)` | `void` |
| `buildRegExpStr` | `buildRegExpStr()` | `string` |

## Properties

| Property | Type |
|---|---|
| `#index` | `number` |
| `#varIndex` | `number` |
| `#children` | `Record<string, Node>` |

## Where it refuses work

- `Node` stops the work with an early return when `regexpStr === '.*'`.
- `Node` stops the work with an early return when `/\((?!\?:)/.test(regexpStr)`.
- `Node` stops the work with an early return when `regexpStr.length === 1 && regExpMetaChars.has(regexpStr)`.
- `Node` stops the work with an early return when `(regexpStr.length > 1 || k.length > 1) && k !== ONLY_WILDCARD_REG_EXP_STR && k !== TAIL_W…`.
- `Node` stops the work with an early return when `k.length > 1 && k !== ONLY_WILDCARD_REG_EXP_STR && k !== TAIL_WILDCARD_REG_EXP_STR`.
- `Node` stops the work with an early return when `node.#index !== undefined`.

## Diagram

```mermaid
graph LR
  Route[Route definition] --> Insert[Node.insert]
  Insert --> Tree[Node route structure]
  Tree --> Build[Node.buildRegExpStr]
  Build --> Pattern[Regular expression source]
  Pattern --> Matcher[Route matcher]
```

## Usage

```ts
import { Node } from './node'

const handler = () => new Response('User route matched')

// A router creates and owns the root Node instance.
function compileRoutes(node: Node) {
  node.insert('GET', '/users/:id', handler)

  const patternSource = node.buildRegExpStr()
  return new RegExp(patternSource)
}
```

## AI Coding Instructions

- Treat `Node` as router-internal state; register routes through the router when that public API is available.
- Call `insert()` before `buildRegExpStr()`, since the generated pattern reflects the routes stored in the node.
- Keep route parameter syntax consistent with the regular-expression router's parser.
- Preserve route insertion behavior when changing node traversal or pattern generation, as matcher output depends on stored route structure.

## Used by

1 reference from 1 file. Each is a place in this repository where the symbol is actually used — go read one rather than trusting an example.

### Imported by (1)

- `ReplacementMap` — `src/router/reg-exp-router/trie.ts`:4