How to solve vue data hijacking

How to solve Vue data hijacking?

Vue is a very popular front-end framework, often used for SPA (single page application) development. One of its core features is data binding (data-driven), which uses data binding to achieve component development. .

Data binding is one of the core features of the Vue framework. Vue uses data hijacking technology to achieve two-way data binding. In Vue, if we modify the data in the data model, the view will automatically update, and vice versa. But how to solve the problems caused by data hijacking?

The principle of Vue data hijacking

When Vue uses two-way data binding, the data will be hijacked. For example, we use a double bracket ({{}}) in the template to bind Data, as shown below:

<div>
  {{message}}
</div>

In Vue, this binding method is called "template binding", and then Vue will use all this binding method in the "template compilation phase" Replace the JavaScript code as follows:

var data = { message: 'Hello,Vue!' };  
var app = new Vue({
  el: '#app',
  data: data
});

This code will transfer all the properties in the data object we defined to the Vue instance, and then execute the following code:

Object.keys(data).forEach(key => {
  proxyData(this, key, data[key]);
});

Among them, the proxyData method is a custom method, mainly used to implement data hijacking. Data hijacking is mainly reflected in Vue instance objects.

The specific hijacking process is as follows:

1. Vue will use the Object.defineProperty() method to hijack all properties on the data object.

function proxyData (vm, key, val) {
  Object.defineProperty(vm, key, {
    configurable: false,
    enumerable: true,
    get () {
      console.log(`get ${val}`);
      return val;
    },
    set (newVal) {
      console.log(`set ${newVal}`);
      val = newVal;
      // 触发diff算法 - 更新页面
      vm.$nextTick(() => {
        // 触发更新
      });
    }
  });
}

2. In the get function, Vue will add the observer object to the subscriber queue. When data changes, the observer object is notified and updates the UI.
3. In the set function, Vue will notify the observer object of the data modification, and the observer object will re-render the UI.
4. Vue uses virtual DOM (Virtual DOM) to achieve efficient DOM operations, avoiding the performance bottleneck caused by directly operating the DOM.

The problem of Vue data hijacking

Although Vue implements two-way data binding through data hijacking, this method also brings some problems.

1. The new attribute of the object cannot be monitored

When we used Vue, we found that if we add a new attribute to the object in the data model, then this attribute cannot be monitored. Observed, that is to say, the modification of this property will not trigger the re-rendering of the view. Only properties that exist when the object is initialized can be observed.

var app = new Vue({
  el: '#app',
  data: {
    obj: { a: 1, b: 2 }
  }
});

// 需要新增c属性
app.obj.c = 3;

// 修改c属性，视图不会更新
app.obj.c = 4;

2. Array operations cannot be monitored

Vue cannot monitor array modifications, such as push, pop, shift and unshift operations. We can only use Vue to provide Special methods to make changes, such as: Vue.set() and Vue.delete().

var app = new Vue({
  el: '#app',
  data: {
    arr: [1, 2, 3]
  }
});

// 只能使用Vue提供的特殊方法进行数组的操作
 Vue.set(app.arr, 3, 4);

Such an operation is obviously inconvenient. We can use a library to solve this problem. The name of this library is vuex.

Vuex is a state management library specially developed for Vue. It can help us centrally manage the data model and share the same state between multiple components, thus facilitating our state management in Vue.

Through Vuex, we can divide multiple components with shared data into a tree-structured state manager. When a component wants to modify a certain attribute, it needs to submit an Action to indirectly The method of triggering Mutation locally. What Mutation can change is State. When State changes, all components that depend on this State are automatically updated.

3. Long list performance issues

In Vue, if we have a long list, when one of the data changes, it will cause all the data in the entire list to change. The data is all re-rendered, which can cause performance problems. In order to solve this problem, Vue provides a key attribute. We can give each object in the list a key value, so that when the data changes, only the changed item will be re-rendered, not the entire list.

<template>
  <div>
    <li v-for="(item, index) in list" :key="item.id">{{item.name}}</li>
  </div>
</template>

Summary

Vue uses data hijacking to implement two-way data binding, but this method will bring some problems, such as the inability to monitor new properties of objects and the inability to handle changes in arrays wait. But there are many ways to solve these problems in Vue, such as using key attributes to improve the performance of list rendering, using Vuex for state management, etc. We need to choose the most appropriate method to solve the problems that Vue data hijacking may cause.

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