What is the relationship between export default and ES module in Vue

export default is the main way to export modules in Vue. It simplifies component export and import, and one module can only have one export default, which makes the code more concise. It is often used to export single file components, but it also has limitations such as the inability to export multiple content.

export default and ES modules in Vue: closer than you think

You may have seen export default in countless Vue projects, but you are vague about its relationship with the ES module. This article will dig deeper and keep you from getting confused by them anymore. After reading it, you will understand the nature of export default and how it elegantly collaborates with the ES module mechanism to build a clearer and easier to maintain Vue application.

Let's start with the ES module. The ES module is a standard module system for JavaScript that provides a way to share code among different JavaScript files. The core lies in import and export keywords. export is used to export variables, functions or classes in modules so that other modules can access; import is used to import content exported by other modules.

Now, let's focus on export default . It is actually a special export method, and a module can only have one export default . It does not require a name specified like a name export ( export const foo = ... ) and you can give it any name you like when importing. This is very common in Vue single file components (.vue), because a component usually has only one default export, representing the component itself.

Let’s take a look at an example, a simple Vue component:

 <code class="javascript">// MyComponent.vue export default { name: 'MyComponent', data() { return { message: 'Hello from MyComponent!' }; }, template: `<div>{{ message }}</div>` };</code>

In this example, the entire component object is exported by export default . In another component, you can import it like this:

 <code class="javascript">// AnotherComponent.vue import MyComponent from './MyComponent.vue'; export default { components: { MyComponent }, // ... rest of the component };</code>

Here, MyComponent can be any legal variable name. This is exactly the convenience of export default , which simplifies the import process and makes the code more concise.

But export default is not perfect either. One limitation of it is that a module can only have one export default . If you need to export multiple content, you must use named export. This may limit flexibility in some cases. In addition, using export default will make the intent of the code slightly less clear, especially when the project is larger, it may take more time to track the specific content of export default . Named exports are, by contrast, more readable and maintainable.

To go deeper, let's see how Vue handles export default internally. Vue's compiler recognizes export default and uses it as the root object of the component. This object contains various properties of the component, such as data , methods , template , etc. The Vue framework creates and renders component instances based on this object.

To sum up, export default plays a key role in Vue, which simplifies the export and import of components and makes the code easier to read and maintain, especially in the case of single-file components. However, it also has certain limitations, and it is necessary to choose a suitable export method according to actual conditions. If you need to export multiple content, or pursue higher code clarity, then naming exports will be a better choice. Only by mastering these two export methods can you write more elegant and efficient Vue code. Remember, choosing the most important thing is to choose a solution that suits your project needs. Don’t blindly pursue so-called “best practices”, but understand the principles and trade-offs behind them.

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