Function updateElements

packages/next/src/client/head-manager.ts:53–100

(type: string, components: JSX.Element[])

}

function updateElements(type: string, components: JSX.Element[]) {
  const headEl = document.querySelector('head')
  if (!headEl) return

  const oldTags = new Set(headEl.querySelectorAll(`${type}[data-next-head]`))

  if (type === 'meta') {
    const metaCharset = headEl.querySelector('meta[charset]')
    if (metaCharset !== null) {
      oldTags.add(metaCharset)
    }
  }

  const newTags: Element[] = []
  for (let i = 0; i < components.length; i++) {
    const component = components[i]
    const newTag = reactElementToDOM(component)
    newTag.setAttribute('data-next-head', '')

    let isNew = true
    for (const oldTag of oldTags) {
      if (isEqualNode(oldTag, newTag)) {
        oldTags.delete(oldTag)
        isNew = false
        break
      }
    }

    if (isNew) {
      newTags.push(newTag)
    }
  }

  for (const oldTag of oldTags) {
    oldTag.parentNode?.removeChild(oldTag)
  }

  for (const newTag of newTags) {
    // meta[charset] must be first element so special case
    if (
      newTag.tagName.toLowerCase() === 'meta' &&
      newTag.getAttribute('charset') !== null
    ) {
      headEl.prepend(newTag)
    }
    headEl.appendChild(newTag)
  }
}

export default function initHeadManager(): {
  mountedInstances: Set<unknown>