Detailed explanation of Vue computed properties and their application scenarios

Vue is a popular JavaScript framework that helps developers build dynamic user interfaces in web applications. Vue components are reusable UI elements composed of templates, data and methods, and computed properties are an important element in Vue applications. This article will provide an in-depth introduction to the details of Vue computed properties, including their syntax and common application scenarios.

Definition of computed properties

A computed property is a data object in a Vue application, which provides a convenient way to handle complex calculations and logical operations based on data. Computed properties themselves are reactive; they automatically recalculate and update when the associated data changes.

The syntax of calculated properties

The syntax of calculated properties is very simple. The following is a basic syntax example:

new Vue({
  el: '#app',
  data: {
    message: 'Hello Vue.js!'
  },
  computed: {
    reversedMessage: function() {
      return this.message.split('').reverse().join('')
    }
  }
})

In the above example, we define a calculated property reversedMessage, which gets the value of message, flips it and returns it. By calling the computed property on the Vue instance, we define the computed property and specify the data properties it depends on.

Advantages of computed properties

Using computed properties has the following advantages:

1. Computed properties will be cached.

An important feature of computed properties is that they are cached. If the data property that a computed property depends on has not changed, the value of the computed property will not be recalculated. This caching can greatly improve the performance of Vue applications.

2. Computed properties can reduce the code in the template.

When we need to perform complex data calculations or logical operations, computed properties allow us to abstract these operations, making the code in the template more concise and easy to understand.

3. Calculated properties can be shared with other calculated properties.

Computed properties can be dependent on other calculated properties, which allows us to build more flexible and reusable code structures.

Application scenarios of computed properties

The following are some common application scenarios of Vue computed properties:

1. Filtering and sorting

We can use computed properties to filter and sort list data. For example, we can define a computed property that will filter out all empty or unwanted data.

computed: {
  filteredList: function() {
    return this.list.filter(function(item) {
      return item && item.name && item.name.trim() !== ''
    })
    .sort(function(a, b) {
      return a.name.toLowerCase() > b.name.toLowerCase()
    })
  }
}

In the above example, we defined a calculated property named filteredList, which will return a filtered and sorted list data.

2. Format data

We can use calculated properties to format data, such as formatting currency, date and time, etc. As shown below:

computed: {
  formattedPrice: function() {
    return '$' + this.price.toFixed(2)
  },

  formattedDate: function() {
    return moment(this.date).format('MMMM D, YYYY')
  }
}

In the above example, we have defined two calculated properties called formattedPrice and formattedDate. They format currency and date data respectively.

3. Getters and setters of calculated properties

We can use the getter and setter methods of calculated properties to achieve more flexible property calculations. For example, we can define a computed property that will automatically update the associated data when we assign a value to it. As shown below:

computed: {
  fullName: {
    get: function() {
      return this.firstName + ' ' + this.lastName
    },
    set: function(newValue) {
      var names = newValue.split(' ')
      this.firstName = names[0]
      this.lastName = names[names.length - 1]
    }
  }
}

In this example, we have defined a computed property named fullName which has getter and setter methods. When we get the property, it combines firstName and lastName into a complete name; and when we set the property to some new value, it combines the The value is split into first name and last name and automatically updated on the firstName and lastName properties.

Conclusion

Vue computed properties are a very useful element in Vue applications that can help us simplify data processing and logical operations. They can greatly improve the readability and usability of our code. When developing Vue applications, we should try to use computed properties to simplify data manipulation.

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