How to use watch to monitor changes in objects in Vue

Vue.js is a popular front-end framework, and one of its core concepts is "responsive data binding". When the data attribute in the component changes, Vue.js will automatically update the UI interface. However, sometimes we need to perform some specific operations when the data changes. In this case, we can use the watch function in Vue.

In Vue, watch is an option that can be used to monitor changes in objects and execute corresponding functions. In this article, we will introduce how to use watch to monitor changes in objects.

First, we need to declare the properties of one or more objects in the Vue component. For example, we declare an object named "user" that includes the "name" and "age" properties:

data() {
  return {
    user: {
      name: 'Alice',
      age: 30
    }
  }
}

Next, we need to create a watch option in the component's watch property for Monitor changes in object properties. For example, we can listen to the "age" property of the "user" object:

watch: {
  'user.age'(newValue, oldValue) {
    console.log(`User's age changed from ${oldValue} to ${newValue}`);
  }
}

In the above code, we create a function called "watcher" which contains two parameters: "newValue" and "oldValue". These parameters will contain the new and old values ​​of the property so that we can compare between them and perform appropriate actions. For example, we print out a message in the function indicating that the "age" property of the "user" object has changed.

It is worth noting that we use the string form of "user.age" to monitor the "age" attribute of the "user" object. This is because object properties are usually reactive, so Vue will convert the name of the object property into a reactive update path. In this case, we need to use string form to listen for changes in object properties.

In addition to monitoring changes in object properties, we can also monitor changes in the entire object. For example, we can use the following code to listen for any changes in the "user" object:

watch: {
  user: {
    handler(newValue, oldValue) {
      console.log('User object changed:', newValue);
    },
    deep: true
  }
}

In the above code, we have created a "handler" function that will be called whenever the "user" object changes . Similar to the first example, we pass the new and old values ​​as function parameters and print the message in the function.

In addition, we also set the "deep" option to true to deeply monitor changes in the object. This means that Vue will recursively listen for changes in nested values ​​of objects.

Finally, we need to modify the value of the "user" object to trigger the watch function. For example, we can use the following code to increment the "age" property of the "user" object:

this.user.age += 1;

When we run the above code, the watch function will be called and the corresponding message will be printed in the console.

Summary: In Vue, we can use the watch option to listen for changes in objects and execute corresponding functions. This allows us to perform specific actions when the data changes, such as updating the UI or sending an HTTP request. When we use watch, we need to ensure that the data is modified at the right time to trigger the watch function.

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