feat: add getBasePath() public method

[G4brym]

Summary

Adds a getBasePath() public method to the Hono class, exposing the current base path of a Hono instance without relying on the private _basePath property.

Motivation

Currently, the only way to read a Hono instance's base path at runtime is by accessing the private _basePath property. This is fragile — it's not part of the public API and could break without notice.

Libraries that integrate with Hono (such as chanfana, an OpenAPI schema generator) need to detect the base path to correctly generate API documentation and route schemas. Right now, chanfana reads _basePath defensively with runtime type guards (see PR), but a proper public API would be much better.

Changes

• src/hono-base.ts — Added getBasePath(): string method on HonoBase that returns the current _basePath value
• src/hono.test.ts — Added 4 tests:
  • Returns "/" for a fresh instance
  • Returns the base path after basePath()
  • Returns the merged path after chained basePath() calls
  • Original instance is unaffected after basePath() creates a clone

Usage

const app = new Hono().basePath('/api')
app.getBasePath() // '/api'

const v1 = app.basePath('/v1')
v1.getBasePath()  // '/api/v1'
app.getBasePath()  // '/api' (unchanged)

All 205 tests in src/hono.test.ts pass.

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This PR was generated with AI assistance (OpenCode).

[yusukebe]

Hey @G4brym

If you want to get a base path in a handler, you can use the basePath() in the Route Helper: https://hono.dev/docs/helpers/route#basepath

Have you checked it?

[G4brym]

Hey @yusukebe, thanks for the pointer!
I checked that, but it requires a Context (c) and only works inside a request handler
my use case is different, I need the base path at setup time, outside of a request

for example:

const app = new Hono().basePath('/api')                                                                                                                                                                                                                                                                              
const router = fromHono(app)  // ← need to know "/api" here, no `c` exists yet 

[G4brym]

or maybe the basePath helper function could be updated to also work with Hono apps, like:

import {
  basePath,
} from 'hono/route'

const subApp = new Hono()
const path = basePath(subApp) // '/api'

app.route('/:sub', subApp)

i can update the pr if you agree with this change