vue prohibits data linkage

Vue is a popular JavaScript framework whose core purpose is to make front-end development easier and faster. One of the most commonly used concepts in the Vue framework is data linkage, which makes the data in the application very sensitive and dynamic to user behavior.

However, sometimes, developers may want to prohibit data linkage and only allow certain data to change under specific conditions. The most common situation is data restriction and filtering.

This article will introduce how to disable data linkage in Vue, and only hope to support data linkage under certain special circumstances.

1. What is data linkage

In Vue, data linkage means that when a piece of data changes, all data related to it will also be updated. This linkage mechanism can be achieved through Vue's responsive system.

Vue’s reactive system means that when we pass an object to a Vue instance as data, Vue will add its own properties to the object to track property changes in the object. When this property is set to a new value, Vue will notify the component to re-render the template.

For example, suppose we have an object in a Vue instance:

data: {
  user: {
    name: 'John Doe',
    age: 30
  }
}

When we update the value of user.age through code, Vue will automatically update the following of the component Two places:

1. The place where this property is displayed;
2. Any calculator properties that depend on this property.

This is data linkage. When user.age changes, not only the property itself will change, but also other properties and calculator properties involved in it will be updated.

2. Scenarios where data linkage is prohibited

Although data linkage can bring great convenience, sometimes it may become a burden for us. In some cases, disabling data linkage may be more appropriate, such as:

1. Data filtering

When we need to filter some content in the data, disabling data linkage may be necessary of. For example, we may want to only enter numbers in the input box and not accept non-numeric characters. In this example, setting the v-model of an input box will cause all input to become strings, which does not meet our requirements. We need to convert it and then process it through JavaScript code.

2. Restrict data from entering a specific state

Sometimes we want data to only be allowed to change under specific conditions. For example, a user's date of birth can only be updated when he/she turns 18. Here, we need to disable data linkage to ensure that the data will only change when the conditions are met.

3. Business logic rules

In some cases, we need to process and update data according to specific business logic rules. This may involve the calculation of multiple attributes, data validation, and some other specific scenarios. In this case, disabling data linkage is necessary to ensure more complete and accurate processing and updating of data.

Now we have figured out why we need to disable data linkage. Next, let's see how to do this in Vue.

3. Technical implementation of disabling data linkage

The implementation technology of disabling data linkage in Vue is very simple. Just use the $set and $watch methods provided by Vue itself.

1. Use the $set method

Vue’s $set method allows us to dynamically add a property to an existing object. This method bypasses the reactive system in Vue, allowing us to control changes to properties without causing changes to other associated properties.

In the following code example, we have a Vue instance with an object property named user. We want to set the age property in the user object to a new value, and we don't want this change to cause related data to respond. Implementing this method is simple:

# 禁止数据联动的代码

export default {
  data() {
    return {
      user: {
        name: 'John Doe',
        age: 30
      }
    }
  },
  methods: {
    updateAge(value) {
      // 使用 $set 方法更新 user 对象的 age 属性
      this.$set(this.user, 'age', value)
    }
  }
}

This way, whenever we call the updateAge method, we can control the changes to user.age.

2. Use the $watch method

Vue’s $watch method can observe changes in a property in the component and call a function in response. Using this method, we can control attribute changes and prevent data linkage from occurring.

In the following code example, we have a Vue instance with an object property named user. We want to be able to change the age attribute value in the user object only under certain conditions. To implement this method, we need to use the $watch method to monitor user.age. When a property is updated, we check if the condition is met. If it doesn't match, we just need to change the property back to its previous value.

# 使用 $watch 方法阻止数据联动

export default {
  data() {
    return {
      user: {
        name: 'John Doe',
        age: 30
      }
    }
  },
  watch: {
    'user.age'(newValue, oldValue) {
      if (newValue < 18) {
        // 如果新值不合法，则将属性设置回旧值
        this.user.age = oldValue
      }
    }
  },
  methods: {
    updateAge(value) {
      this.user.age = value
    }
  }
}

In this way, when updateAge is called, the $watch method will determine whether the attribute change is legal according to the set rules. If the changes meet the requirements, the new value is set into the user object. If the requirements are not met, the $watch method returns the changed property value to its previous value.

Summarize

Disabling data linkage is very necessary in certain scenarios and can effectively help us avoid some unexpected problems. There are many ways to disable data linkage in Vue. This article mainly introduces the use of $set and $watch methods, which are the most popular implementation technologies in Vue. When you need to implement similar data restrictions and filtering operations in Vue, you can easily use these methods to control data changes and prevent data linkage from occurring.

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