element-plus/packages/hooks/use-restore-active/index.ts

import { isRef, watch } from 'vue'
import type { Ref } from 'vue'

/**
 * This method provides dialogable components the ability to restore previously activated element before
 * the dialog gets opened
 */
export default (toggle: Ref<boolean>, initialFocus?: Ref<HTMLElement>) => {
  let previousActive: HTMLElement
  watch(() => toggle.value, val => {
    if (val) {
      previousActive = document.activeElement as HTMLElement
      if (isRef(initialFocus)) {
        initialFocus.value.focus?.()
      }
    } else {
      if (process.env.NODE_ENV === 'testing') {
        previousActive.focus.call(previousActive)
      } else {
        previousActive.focus()
      }
    }
  })
}