Vue mixins is the way to reuse component logic. When multiple components have duplicate logic, they can be extracted into the mixin and reuse through merge options, such as life cycle hooks and methods will be executed sequentially (mixin first and component later). 1. Used to reuse logic, organize code, and extend functions; 2. Pay attention to naming conflicts, state pollution, and maintenance complexity; 3. Vue 3 It is recommended to use Composition API to replace mixin, but the Vue 2 project can still be used effectively.

Vue mixins is a flexible way to reuse component logic. When you find duplicate option logic in multiple Vue components (such as methods, life cycle hooks, data, etc.), you can extract these common parts into a mixin and then "mix" it in the required components.

It's a bit like packing a commonly used piece of code into a small module, using it as you need it, without repeating the same logic.

What is Mixin?

Mixin is an ordinary JavaScript object that can contain any component options, such as data , methods , created life cycle hook, etc.

When a component uses a mixin, all properties and methods in this mixin are "merged" into the component itself. In other words, the component will have the data, methods, life cycle and other content provided by the mixin.

To give a simple example:

 const myMixin = {
  created() {
    console.log('This life cycle comes from mixin');
  },
  methods: {
    sayHello() {
      console.log('Hello from mixin!');
    }
  }
}

Then use it in the component like this:

 export default {
  mixins: [myMixin],
  created() {
    console.log('component' created');
  }
}

After running, you will find that both created will be called in the order: first execute the mixin, and then execute the component's own.

What can Mixin do?

• Reuse logic : such as form verification, data initialization, event listening.
• Organize code structure : centrally manage some general logic to avoid over-bloat components.
• Extended component functions : such as adding a global method or computed property.

Common uses include:

• Unified processing of form controls
• Unified data requests when page loads
• Public UI state control (such as loading state)
• Multi-component sharing tool method

Notes on using Mixin

Although mixin is very convenient, there are several places that are easy to get stuck in:

• Naming conflict problem : If the mixin is the same as the data and methods in the component, the mixin will "overwrite" the mixin. For example, if the component defines a sayHello() method and mixin also defines a method with the same name, then the final execution of the component's own version.

• State pollution risk : If the object you return in the data function of the mixin does not create a new object at a time, it may cause multiple component instances to share the same state. For example:

 // Error example const badMixin = {
  data() {
    return sharedData; // This sharedData is an externally defined variable}
}

The correct approach is to make sure each component instance has its own independent state copy.

• Maintenance complexity increases : When mixins are used in a large number of them, especially when multiple mixins are nested, the logic may become difficult to track and not very intuitive to debug.

Comparison between Mixin and Composition API

Vue 3 launched the Composition API, where setup() and composables have become more recommended logical multiplexing methods. Compared to mixin, their benefits are:

• See more clearly where to use what logic
• No naming conflict problem
• Easier to test and maintain

However, for Vue 2 or projects that are used to the Options API, mixin is still a very practical tool.

Basically that's it. Using mixin rationally can help you reduce duplicate code and improve development efficiency, but in large projects, you should pay attention to controlling the scope of use to avoid making the logic confused.

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