How to collaboratively optimize application performance through Vue's computed attribute and watch attribute

How to collaboratively optimize application performance through Vue's computed properties and watch properties

Introduction:
Vue is a progressive JavaScript framework for building user interfaces. Its core concept is to combine data and views Perform two-way binding. In actual development, we often need to process some data that requires real-time calculation or monitoring, such as form validation, data filtering, etc. In order to improve application performance, Vue provides computed attributes and watch attributes to collaboratively handle these requirements. This article will introduce how to use computed attributes and watch attributes to optimize application performance, and give corresponding code examples.

1. Use of computed attribute
The computed attribute allows us to declare some properties based on responsive dependencies and encapsulate the calculation logic in them. Vue will automatically update the values ​​of computed properties based on changes in related dependencies to ensure that they are always up to date.

1.1 Basic syntax
Declaring the computed attribute in the Vue component is very simple. You only need to define a function in the computed attribute of the component. For example:

computed: {
    fullName() {
        return `${this.firstName} ${this.lastName}`;
    }
}

In the above code, we define a computed attribute fullName, which returns the complete name after the combination of firstName and lastName.

1.2 Calculation cache
An important feature of the computed attribute is calculation cache. When the responsive data that a computed attribute depends on changes, the computed attribute will be recalculated and the calculation results will be cached. When the computed property is accessed next time, if no related dependencies have changed, Vue will directly return the cached value without recalculating.

This calculation cache mechanism greatly improves performance, especially when computed properties require large computing resources, such as array filtering operations.

1.3 Example
The following is a sample code using the computed attribute:

<template>
  <div>
    <input v-model="firstName" type="text" placeholder="请输入姓">
    <input v-model="lastName" type="text" placeholder="请输入名">
    <p>{{ fullName }}</p>
  </div>
</template>

<script>
export default {
  data() {
    return {
      firstName: '',
      lastName: ''
    };
  },
  computed: {
    fullName() {
      return `${this.firstName} ${this.lastName}`;
    }
  }
};
</script>

In the above code, we use the v-model directive to combine the two input elements and the data attribute of the component. Two-way binding. Then use {{ fullName }} in the template to display the calculation results. When firstName or lastName changes, Vue will automatically update the value of fullName and render the updated result to the page.

2. Use of watch attribute
The watch attribute allows us to monitor a specific data change and perform corresponding operations when the data changes. Unlike the computed attribute, the watch attribute does not perform calculations, but executes a custom logic after the data changes.

2.1 Basic syntax
Declaring the watch attribute in the Vue component is also very simple. You only need to define a function in the watch attribute of the component. For example:

watch: {
    firstName(newValue, oldValue) {
        console.log(`firstName从${oldValue}变为${newValue}`);
    }
}

In the above code, we define a watch attribute to monitor the change of firstName and print the values ​​before and after the change when it changes.

2.2 In-depth monitoring
By default, Vue only monitors changes in direct properties of objects or arrays. If you need to deeply monitor changes in all attributes in an object or array, you can use the deep attribute in the watch attribute. For example:

watch: {
    obj: {
        handler(newValue, oldValue) {
            console.log('obj发生变化');
        },
        deep: true
    }
}

In the above code, we deeply monitor changes in an object named obj. When any attribute in obj changes, the corresponding processing function will be triggered. This is useful for listening to changes in objects.

2.3 Asynchronous Monitoring
Sometimes we want to perform some asynchronous operations after data changes, such as sending requests or updating caches. Vue allows defining an asynchronous function called handler in the watch attribute to handle this situation. For example:

watch: {
    firstName(newValue, oldValue) {
        this.debouncedGetData();
    }
},
methods: {
    debouncedGetData: debounce(function() {
        // 异步操作
    }, 500)
}

In the above code, we use the debounce function in the lodash library to limit the frequency of calling this.debouncedGetData to ensure that only one asynchronous operation is performed within 500 milliseconds.

3. Collaborative use of computed attributes and watch attributes
Computed attributes and watch attributes can be used collaboratively, and they are not mutually exclusive. In actual development, we can flexibly choose one of the two according to different needs, or use both at the same time.

When using the computed attribute, you need to consider the characteristics of the calculation cache, which is suitable for results that rely on other responsive data calculations. When using the watch attribute, it is usually to monitor changes in responsive data and perform corresponding operations, which is suitable for scenarios that require immediate response to data changes.

For example, we can use the computed attribute to calculate the total price of a shopping cart:

computed: {
    totalPrice() {
        return this.cart.reduce((total, product) => total + product.price * product.quantity, 0);
    }
}

And use the watch attribute to monitor the change in the quantity of a product in the shopping cart and update it when it changes Total price:

watch: {
    'cart': {
        handler(newValue, oldValue) {
            this.totalPrice = this.cart.reduce((total, product) => total + product.price * product.quantity, 0);
        },
        deep: true
    }
}

In the above code, we monitor changes in the shopping cart (cart). When the quantity of a product in the shopping cart changes, the total price (totalPrice) will be recalculated and updated. .

Conclusion:
In Vue development practice, rational use of computed attributes and watch attributes can improve application performance and development efficiency. The computed attribute can save computing resources and implement complex business logic; while the watch attribute can monitor data changes and perform corresponding operations to meet some special needs. Flexible use of these two features according to specific situations can make the code more concise and elegant.

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