vue3 immediate

Vue 3 introduces a new feature called "immediate" to the reactivity system. The "immediate" option allows you to specify whether a reactive effect should be triggered immediately or not. By default, when you create a reactive effect using the `watch` function or the composition API's `watchEffect`, the effect will not be triggered on the first render. However, if you pass `immediate: true` as an option, the effect will be triggered immediately upon creation.

Here's an example of how to use the "immediate" option with the `watch` function:

import { ref, watch } from 'vue';

const count = ref(0);

watch(
  count,
  (newCount, oldCount) => {
    console.log(`Count changed from ${oldCount} to ${newCount}`);
  },
  { immediate: true }
);

In the above example, the effect function will be called immediately with the initial value of `count`, and subsequently whenever `count` changes.

This "immediate" option is useful in scenarios where you want to trigger an effect immediately upon creation, such as fetching initial data or performing an initial setup.