Vue realizes responsive binding through data hijacking combined with publish subscription mode. 1. Use Object.defineProperty (Vue2) or Proxy (Vue3) to hijack data during initialization, and properties can be traced when they are accessed or modified; 2. The template is compiled into a rendering function to generate a virtual DOM; 3. Updates are triggered when data changes, and DOM operations are optimized through asynchronous queues; 4. There are special restrictions on the responsive processing of arrays and objects, and specific methods are required to ensure responsiveness.
Vue's data binding mechanism is one of its most core functions and is also the key to enabling developers to easily synchronize views and data. Simply put, Vue automatically tracks dependencies through a responsive system and updates the DOM when data changes . You don't need to manually operate the DOM, you just need to care about the changes in the data, and the view will be updated automatically.
Let's take a look at how it is done:
Data Hijacking Publish Subscription Model
When Vue initializes data, it uses Object.defineProperty (in Vue2) or Proxy (in Vue3) to "hijack" the properties of the data object. This way, when these properties are accessed or modified, Vue can be perceived.
For example:
data() {
return {
message: 'Hello Vue'
}
} When you access message , Vue can know which components or templates use this variable; when you modify message , it will notify these places to update itself.
This involves publishing subscription mode: when the data changes, it publishes an event, and all places that subscribe to this data will be notified and updated accordingly.
Compile template into rendering function
The HTML you write in the Vue template will actually be compiled into a render function that contains the creation logic of the virtual DOM.
For example, you wrote:
<p>{{ message }}</p>Vue may become a function like this after compilation:
function render() {
return createElement('p', message)
} When message changes, the rendering function is re-executed, a new virtual DOM is generated, and then compared with the previous ones, and only the changed parts are updated. This is the so-called "virtual DOM diff".
Asynchronous update queue
Vue updates to the DOM are asynchronous. In other words, even if you modify the data multiple times in succession, Vue will merge these updates and perform only once in the end to improve performance.
For example:
this.message = 'A' this.message = 'B' this.message = 'C'
Although it has been changed three times, Vue will only update the DOM once in the next "event loop".
You can use Vue.next() or this.$nextTick() to ensure that some code is executed after the DOM is updated.
Note: Responsive processing of arrays and objects
Vue has made special processing on array operations. Modifying array elements directly through indexes (such as arr[0] = newValue ) will not trigger updates. You should use the variant methods provided by Vue (such as push , pop , splice , etc.) or use Vue.set() .
For an object, if you add a new property to the object and this property is not predefined in data, it will not be responsive. Therefore, when defining the data structure, try to write all the fields to be used in advance.
Basically that's it. Understanding Vue's data binding mechanism will not only help you write more efficient code, but also locate the cause faster when debugging problems.
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