A brief analysis of how vue implements watchdeep

Vue.js is a very popular JavaScript framework that makes front-end development easier and faster. Among them, watch is a very important function in Vue.js, which can be used to monitor data changes. In some cases, we need to deeply monitor data changes, in which case we need to use watchDeep. This article will introduce how to implement watchDeep in Vue.js.

1. What is watchDeep

watchDeep can deeply monitor all properties of an object. When any value of an object property changes, it will be captured and corresponding operations will be performed. Compared with ordinary watches, watchDeep can reduce the trouble of manually monitoring object properties and avoid the problem of being unable to monitor after data changes.

2. Why watchDeep is needed

In Vue.js, it is often necessary to monitor the properties of an object, usually using watch. However, when the monitored object is too complex and has many attributes, it is obviously unrealistic to manually monitor all attribute changes.

At this time, watchDeep comes in handy. It can deeply monitor all property changes of an object, thereby avoiding the need to manually monitor all properties.

3. How to implement watchDeep

The following will introduce two methods to implement watchDeep:

1. Recursively monitor all attributes

First , we need to define a method to traverse all properties of the object and set the listener. This method can be implemented recursively. The specific code is as follows:

function deepWatch (obj, callback) {
    Object.keys(obj).forEach(key => {
        if (typeof obj[key] === 'object') {
            deepWatch(obj[key], callback)
        }
        Object.defineProperty(obj, key, {
            configurable: true,
            enumerable: true,
            get() {
                return this['_' + key]
            },
            set(val) {
                this['_' + key] = val
                callback()
            }
        })
    })
}

This method uses the Object.defineProperty() method, which can define the properties of the object as getters and setters. When the property value changes, the setter method will be triggered to perform the corresponding operation. All properties are also monitored recursively here.

To use this method to monitor changes in an object, you only need to call the deepWatch() method and pass in the object to be monitored and the changed callback method.

2. Watch implementation based on Vue.js

In addition to the above methods, you can also use the watch inside Vue.js to deeply monitor object changes. The specific code is as follows:

new Vue({
    data: {
        obj: {
            name: '',
            age: '',
            address: {
                province: '',
                city: '',
                district: ''
            }
        }
    },
    watch: {
        obj: {
            handler: function(val) {
                this.$emit('objChanged', val)
            },
            deep: true
        }
    }
})

This method is implemented based on the watch function of Vue.js. The obj object is defined in the data attribute, and the watch option of the Vue instance is used to monitor changes in the obj attribute. Deep is set to true, which means To deeply monitor all properties of the obj object.

When any property of the obj object or its sub-properties changes, the handler method will be triggered and the objChanged event will be triggered. Corresponding operations can be performed in the callback function.

This method is simpler and more efficient, and does not require manual traversal of all properties. However, it should be noted that the watch mechanism of Vue.js cannot monitor changes in array elements and needs to be processed using the methods provided by Vue.js alone.

4. Summary

In the Vue.js development process, watchDeep is a very important function, which can avoid manually monitoring all object properties. There are two ways to implement watchDeep, recursively monitoring all properties and Vue.js-based watch implementation. The former requires manually writing code to monitor the object's property values, and recursively traverses all properties; the latter uses Vue.js's built-in watch to achieve a simpler and more efficient implementation.

No matter which method is used, in-depth monitoring of object property changes is a very important skill in Vue.js development, which can avoid a lot of trouble and improve development efficiency.

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