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Vue 3.0 reactive computation and listening

In Vue 3.0, you can perform reactive computation and listening through several features, primarily ref, reactive, and computed. Here's a tutorial showcasing how you can use these features:

Step 1: Initialize your Vue project.

Create a new Vue 3 project using Vue CLI.

vue create my-project

Choose Vue 3 when asked which version of Vue to use.

Step 2: In your component, import ref, reactive, and computed from vue.

<template>
  <div>
    <input v-model="person.name">
    <p>Full name: {{ fullName }}</p>
  </div>
</template>

<script>
import { ref, reactive, computed } from 'vue';

export default {
  setup() {
    const person = reactive({
      name: 'John Doe',
      lastName: 'Smith'
    });
    
    const fullName = computed(() => `${person.name} ${person.lastName}`);

    return {
      person,
      fullName
    };
  },
};
</script>

In this example, we use the reactive function to create a reactive object called person. person has two properties: name and lastName. We then use the computed function to create a computed property fullName. fullName is a function that returns the full name of the person, which is the concatenation of person.name and person.lastName. This computed property is reactive, which means it will automatically update whenever person.name or person.lastName changes.

The setup method is a new component option in Vue 3.0 that serves as the entry point for using the Composition API within components.

Step 3: Run your application.

You can run your Vue 3 application with the following command:

npm run serve

You should see an input box pre-populated with 'John Doe'. As you change the name in the input box, you will see the full name also updates automatically, demonstrating the reactive computations and listening.

The ref function can be used similarly to create a reactive reference. The main difference is that ref is used for primitive data types (like string, number) whereas reactive is used for objects.

Vue 3.0 watchEffect Function:

Description: watchEffect is a function that automatically tracks reactive dependencies and executes its callback when any of those dependencies change.

Code Example:

<script>
import { ref, watchEffect } from 'vue';

export default {
  setup() {
    const count = ref(0);

    watchEffect(() => {
      console.log(`Count changed: ${count.value}`);
    });

    return {
      count,
    };
  },
};
</script>

Vue 3.0 watch Function:
- Description: watch is a function that allows for more fine-grained control over reactive dependency tracking and offers before and after hooks.
- Code Example:
```
watch(
  () => count.value,
  (newValue, oldValue) => {
    console.log(`Count changed from ${oldValue} to ${newValue}`);
  }
);
```
Vue 3.0 Watching Multiple Properties:
- Description: You can watch multiple properties by providing an array of dependencies.
- Code Example:
```
watch([() => prop1, () => prop2], ([newProp1, newProp2], [oldProp1, oldProp2]) => {
  // Handle changes
});
```
Reactive Data Binding in Vue 3.0 Templates:
- Description: Reactive data can be directly bound to templates using ref or accessed through the value property.
- Example:
```
<template>
  <div>{{ count }}</div>
</template>
```
How to Use ref in Vue 3.0:
- Description: ref is used to create a reactive reference to a value.
- Code Example:
```
const count = ref(0);
```