vue3-core/packages/runtime-dom/src/index.ts

import {
  createRenderer,
  warn,
  RootRenderFunction,
  CreateAppFunction
} from '@vue/runtime-core'
import { nodeOps } from './nodeOps'
import { patchProp } from './patchProp'
// Importing from the compiler, will be tree-shaken in prod
import { isFunction, isString, isHTMLTag, isSVGTag } from '@vue/shared'

const { render: baseRender, createApp: baseCreateApp } = createRenderer({
  patchProp,
  ...nodeOps
})

// use explicit type casts here to avoid import() calls in rolled-up d.ts
export const render = baseRender as RootRenderFunction<Node, Element>

export const createApp: CreateAppFunction<Element> = (...args) => {
  const app = baseCreateApp(...args)

  if (__DEV__) {
    // Inject `isNativeTag`
    // this is used for component name validation (dev only)
    Object.defineProperty(app.config, 'isNativeTag', {
      value: (tag: string) => isHTMLTag(tag) || isSVGTag(tag),
      writable: false
    })
  }

  const { mount } = app
  app.mount = (container): any => {
    if (isString(container)) {
      container = document.querySelector(container)!
      if (!container) {
        __DEV__ &&
          warn(`Failed to mount app: mount target selector returned null.`)
        return
      }
    }
    const component = app._component
    if (
      __RUNTIME_COMPILE__ &&
      !isFunction(component) &&
      !component.render &&
      !component.template
    ) {
      component.template = container.innerHTML
    }
    // clear content before mounting
    container.innerHTML = ''
    return mount(container)
  }

  return app
}

// DOM-only runtime directive helpers
export {
  vModelText,
  vModelCheckbox,
  vModelRadio,
  vModelSelect,
  vModelDynamic
} from './directives/vModel'
export { withModifiers, withKeys } from './directives/vOn'
export { vShow } from './directives/vShow'

// DOM-only components
export { Transition, TransitionProps } from './components/Transition'
export {
  TransitionGroup,
  TransitionGroupProps
} from './components/TransitionGroup'

// re-export everything from core
// h, Component, reactivity API, nextTick, flags & types
export * from '@vue/runtime-core'