How to use computed in Vue to monitor changes in multiple data

Vue is a popular front-end framework that provides a method for building user interfaces. Data management in Vue is provided by components, each component has its own state and logic. In Vue, we can use the computed attribute to define a responsive computed property. The computed attribute can automatically update its value based on changes in other data. Therefore, in some cases, we can use the computed attribute to listen for changes in multiple data. In this article, we will introduce how to use the computed attribute in Vue to monitor changes in multiple data.

In Vue, we can use the computed attribute to define a computed property. A computed property is a property that depends on other data and its value is calculated based on other data. The computed attribute can automatically update its value based on changes in other data, and has a caching mechanism that will only be recalculated when the dependent data changes. Computed properties can be used like normal properties. We can access the data and methods of the current component through this.

The following is a simple example of using the computed property:

<template>
  <div>
    {{fullName}}
  </div>
</template>

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

In the above example, we define a calculated property fullName, which depends on the two data firstName and lastName. The value of fullName is calculated by concatenating firstName and lastName. We use fullName in the component template. When the value of firstName or lastName changes, the value of fullName will also be automatically updated.

In actual development, we may need to monitor changes in multiple data. In this case, we can use the computed attribute. The following is an example of monitoring multiple data changes:

<template>
  <div>
    {{result}}
  </div>
</template>

<script>
export default {
  data() {
    return {
      x: 0,
      y: 0,
      z: 0
    }
  },
  computed: {
    result: {
      get() {
        return this.x + this.y + this.z
      },
      set(val) {
        if (val <= 100) {
          this.x = val / 3
          this.y = val / 3
          this.z = val / 3
        } else {
          console.log('结果不能大于100')
        }
      }
    }
  }
}
</script>

In the above example, we defined a calculated attribute result, which depends on the three data x, y and z. The value of result is calculated by adding the values ​​of x, y, and z. We define both getter and setter in the computed property. Getters are used to get the value of a computed property, and setters are used to set the value of a computed property. When we bind the result through v-model, the setter method of the calculated attribute will be triggered. If the calculated value is greater than 100, a warning message will be output to the console. Otherwise, the x, y, and z of the calculated properties will be evenly distributed according to the calculated results, thereby updating the component's state.

In addition to the above example, we can also use the watch attribute to monitor changes in multiple data. The watch attribute can monitor changes in a certain data and execute a specific function. The difference between it and the computed attribute is that the watch attribute is usually used to monitor changes in data and perform some side effects, while the computed attribute is used to calculate attributes and return a new data.

In Vue, we can use the computed attribute to monitor changes in multiple data. This technique can help us better manage the state of components. Computed attributes can automatically update their values ​​based on changes in other data, and have a caching mechanism. Compared with using watch attributes, using computed attributes can reduce unnecessary calculations and updates.

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