next.js/packages/react-refresh-utils/runtime.ts

import RefreshRuntime from 'react-refresh/runtime'
import RefreshHelpers from './internal/helpers'

export type RefreshRuntimeGlobals = {
  $RefreshReg$: (type: unknown, id: string) => void
  $RefreshSig$: () => (type: unknown) => unknown
  $RefreshInterceptModuleExecution$: (moduleId: string) => () => void
  $RefreshHelpers$: typeof RefreshHelpers
}

declare const self: Window & RefreshRuntimeGlobals

// Hook into ReactDOM initialization
RefreshRuntime.injectIntoGlobalHook(self)

// Register global helpers
self.$RefreshHelpers$ = RefreshHelpers

// Register a helper for module execution interception
self.$RefreshInterceptModuleExecution$ = function (webpackModuleId) {
  var prevRefreshReg = self.$RefreshReg$
  var prevRefreshSig = self.$RefreshSig$

  self.$RefreshReg$ = function (type, id) {
    RefreshRuntime.register(type, webpackModuleId + ' ' + id)
  }
  self.$RefreshSig$ = RefreshRuntime.createSignatureFunctionForTransform

  // Modeled after `useEffect` cleanup pattern:
  // https://react.dev/learn/synchronizing-with-effects#step-3-add-cleanup-if-needed
  return function () {
    self.$RefreshReg$ = prevRefreshReg
    self.$RefreshSig$ = prevRefreshSig
  }
}