How to use the @vue/reactivity.isRef function in @vue/reactivity

cb: WatchCallback | null,
  { lazy, deep, flush, onTrack, onTrigger }: WatchOptions = EMPTY_OBJ
): StopHandle {
  const instance = currentInstance
  const suspense = currentSuspense

  let getter: () => any
  if (isArray(source)) {
    getter = () =>
      source.map(
        s =>
          isRef(s)
            ? s.value
            : callWithErrorHandling(s, instance, ErrorCodes.WATCH_GETTER)
      )
  } else if (isRef(source)) {
    getter = () => source.value
  } else if (cb) {
    // getter with cb
    getter = () =>
      callWithErrorHandling(source, instance, ErrorCodes.WATCH_GETTER)
  } else {
    // no cb -> simple effect
    getter = () => {
      if (instance && instance.isUnmounted) {
        return
      }
      if (cleanup) {
        cleanup()
      }
      return callWithErrorHandling(
        source,

oldRef: string | Function | Ref | null,
    parent: ComponentInternalInstance,
    value: HostNode | ComponentPublicInstance | null
  ) {
    const refs = parent.refs === EMPTY_OBJ ? (parent.refs = {}) : parent.refs
    const renderContext = toRaw(parent.renderContext)

    // unset old ref
    if (oldRef !== null && oldRef !== ref) {
      if (isString(oldRef)) {
        refs[oldRef] = null
        const oldSetupRef = renderContext[oldRef]
        if (isRef(oldSetupRef)) {
          oldSetupRef.value = null
        }
      } else if (isRef(oldRef)) {
        oldRef.value = null
      }
    }

    if (isString(ref)) {
      const setupRef = renderContext[ref]
      if (isRef(setupRef)) {
        setupRef.value = value
      }
      refs[ref] = value
    } else if (isRef(ref)) {
      ref.value = value
    } else if (isFunction(ref)) {
      callWithErrorHandling(ref, parent, ErrorCodes.FUNCTION_REF, [value, refs])
    } else if (__DEV__) {
      warn('Invalid template ref type:', value, `(${typeof value})`)

function setRef(
    ref: string | Function | Ref,
    oldRef: string | Function | Ref | null,
    parent: ComponentInternalInstance,
    value: HostNode | ComponentPublicInstance | null
  ) {
    const refs = parent.refs === EMPTY_OBJ ? (parent.refs = {}) : parent.refs
    const renderContext = toRaw(parent.renderContext)

    // unset old ref
    if (oldRef !== null && oldRef !== ref) {
      if (isString(oldRef)) {
        refs[oldRef] = null
        const oldSetupRef = renderContext[oldRef]
        if (isRef(oldSetupRef)) {
          oldSetupRef.value = null
        }
      } else if (isRef(oldRef)) {
        oldRef.value = null
      }
    }

    if (isString(ref)) {
      const setupRef = renderContext[ref]
      if (isRef(setupRef)) {
        setupRef.value = value
      }
      refs[ref] = value
    } else if (isRef(ref)) {
      ref.value = value
    } else if (isFunction(ref)) {

// unset old ref
    if (oldRef !== null && oldRef !== ref) {
      if (isString(oldRef)) {
        refs[oldRef] = null
        const oldSetupRef = renderContext[oldRef]
        if (isRef(oldSetupRef)) {
          oldSetupRef.value = null
        }
      } else if (isRef(oldRef)) {
        oldRef.value = null
      }
    }

    if (isString(ref)) {
      const setupRef = renderContext[ref]
      if (isRef(setupRef)) {
        setupRef.value = value
      }
      refs[ref] = value
    } else if (isRef(ref)) {
      ref.value = value
    } else if (isFunction(ref)) {
      callWithErrorHandling(ref, parent, ErrorCodes.FUNCTION_REF, [value, refs])
    } else if (__DEV__) {
      warn('Invalid template ref type:', value, `(${typeof value})`)
    }
  }

const oldSetupRef = renderContext[oldRef]
        if (isRef(oldSetupRef)) {
          oldSetupRef.value = null
        }
      } else if (isRef(oldRef)) {
        oldRef.value = null
      }
    }

    if (isString(ref)) {
      const setupRef = renderContext[ref]
      if (isRef(setupRef)) {
        setupRef.value = value
      }
      refs[ref] = value
    } else if (isRef(ref)) {
      ref.value = value
    } else if (isFunction(ref)) {
      callWithErrorHandling(ref, parent, ErrorCodes.FUNCTION_REF, [value, refs])
    } else if (__DEV__) {
      warn('Invalid template ref type:', value, `(${typeof value})`)
    }
  }

s =>
          isRef(s)
            ? s.value
            : callWithErrorHandling(s, instance, ErrorCodes.WATCH_GETTER)
      )

function formatProp(key: string, value: unknown, raw?: boolean): any {
  if (isString(value)) {
    value = JSON.stringify(value)
    return raw ? value : [`${key}=${value}`]
  } else if (
    typeof value === 'number' ||
    typeof value === 'boolean' ||
    value == null
  ) {
    return raw ? value : [`${key}=${value}`]
  } else if (isRef(value)) {
    value = formatProp(key, toRaw(value.value), true)
    return raw ? value : [`${key}=Ref<`, value, `>`]
  } else if (isFunction(value)) {
    return [`${key}=fn${value.name ? `<${value.name}>` : ``}`]
  } else {
    value = toRaw(value)
    return raw ? value : [`${key}=`, value]
  }
}