vite/playground/transform-plugin/vite.config.js

import { resolve } from 'node:path'
import { defineConfig, normalizePath } from 'vite'

const file = normalizePath(resolve(__dirname, 'index.js'))
let transformCount = 1

const transformPlugin = {
  name: 'transform',
  load(id) {
    if (id === file) {
      // Ensure `index.js` is reloaded if 'plugin-dep-load.js' is changed
      this.addWatchFile('./plugin-dep-load.js')
    }
  },
  transform(code, id) {
    if (id === file) {
      // Ensure `index.js` is reevaluated if 'plugin-dep.js' is changed
      this.addWatchFile('./plugin-dep.js')

      return `
        // Inject TRANSFORM_COUNT
        let TRANSFORM_COUNT = ${transformCount++};

        ${code}
      `
    }
  },
}

export default defineConfig({
  plugins: [transformPlugin],
})