Can the export default export data in Vue be modified?

The export default export data in Vue is mutable, and modifying the properties of the exported object will affect all references. However, you must be careful to operate the data returned by the data() function, and should be accessed and modified through component instances to maintain the integrity of the responsive system.

Data variability exported by export default in Vue: truth and trap

Many Vue developers will be confused about a question when using export default to export data: Can the exported data be modified? The answer is: it can be modified, but be careful! This article will dig into this issue in depth and reveal the hidden pitfalls in it. After reading it, you will have a deeper understanding of the data management of Vue components and avoid falling into common pitfalls.

Let's talk about the conclusion first: export default exports a reference to an object, not a copy of the object. This means that if you modify the properties of the exported object itself, the modification is globally visible and all components that reference the object will be affected. But this does not mean that you can modify it at will, especially for objects returned by data() function.

Let's first review the basic structure and data management mechanism of Vue components. The object returned by data() function is the component's responsive data source, which Vue uses to track data changes and update views. export default just exports this component (including the data returned by data() ) for easy use by other modules.

Take an example, suppose we have a component MyComponent.vue :

 <code class="vue"><template> <div>{{ message }}</div> </template> <script> export default { data() { return { message: &#39;Hello, world!&#39; } } } </script></code>

Now, another component AnotherComponent.vue is imported and used by MyComponent :

 <code class="vue"><template> <div> <mycomponent></mycomponent> <p>Message from MyComponent: {{ myMessage }}</p> </div> </template> <script> import MyComponent from &#39;./MyComponent.vue&#39; export default { components: { MyComponent }, data() { return { myMessage: &#39;&#39; } }, mounted() { this.myMessage = MyComponent.data().message; // 直接访问data()，这通常不是一个好主意} }; </script></code>

This code looks fine, but directly accessing MyComponent.data() in the mounted lifecycle function poses a hidden danger. Although the value of message can be obtained, this method breaks Vue's responsive system. Modifying message of MyComponent will not update myMessage in AnotherComponent .

The correct way to do this is to access and modify data through component instances:

 <code class="vue"><template> <div> <mycomponent ref="myComponent"></mycomponent> <p>Message from MyComponent: {{ myMessage }}</p> <button>Change Message</button> </div> </template> <script> import MyComponent from &#39;./MyComponent.vue&#39; export default { components: { MyComponent }, data() { return { myMessage: &#39;&#39; } }, mounted() { this.$nextTick(() => { this.myMessage = this.$refs.myComponent.message; }) }, methods: { changeMessage() { this.$refs.myComponent.message = &#39;Message changed!&#39;; } } }; </script></code>

$refs is used here to get an instance of MyComponent , and then access and modify message through the instance. In this way, Vue's responsive system will work normally and the views will be automatically updated.

Going deeper, if export default exports an object, for example:

 <code class="javascript">export default { foo: 'bar', baz: 123 };</code>

Directly modifying the properties of this object, such as importedObject.foo = 'new bar'; is completely valid, and this modification will affect all modules that import the object.

In short, export default exports references. Modifying the exported object properties will affect all references, but we should avoid directly manipulating the data returned by data() function, but we should operate through component instances to maintain the integrity of the Vue responsive system. Remember that understanding data management mechanisms is the key to writing efficient and maintainable Vue applications. Don't try to bypass Vue's responsive system, this will only cause difficult-to-debugs.

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