Function resolveTarget

packages/runtime-core/src/components/Teleport.ts:45–76

(
  props: TeleportProps | null,
  select: RendererOptions['querySelector'],
)

  typeof MathMLElement === 'function' && target instanceof MathMLElement

const resolveTarget = <T = RendererElement>(
  props: TeleportProps | null,
  select: RendererOptions['querySelector'],
): T | null => {
  const targetSelector = props && props.to
  if (isString(targetSelector)) {
    if (!select) {
      __DEV__ &&
        warn(
          `Current renderer does not support string target for Teleports. ` +
            `(missing querySelector renderer option)`,
        )
      return null
    } else {
      const target = select(targetSelector)
      if (__DEV__ && !target && !isTeleportDisabled(props)) {
        warn(
          `Failed to locate Teleport target with selector "${targetSelector}". ` +
            `Note the target element must exist before the component is mounted - ` +
            `i.e. the target cannot be rendered by the component itself, and ` +
            `ideally should be outside of the entire Vue component tree.`,
        )
      }
      return target as T
    }
  } else {
    if (__DEV__ && !targetSelector && !isTeleportDisabled(props)) {
      warn(`Invalid Teleport target: ${targetSelector}`)
    }
    return targetSelector as T
  }
}

export const TeleportImpl = {
  name: 'Teleport',