A Module Cannot Have Multiple Default Exports

When it comes to working with modules in JavaScript, understanding how default exports function is crucial. One common mistake that many developers encounter is trying to have multiple default exports within a single module. In JavaScript, each module can only have a single default export, and trying to define more than one can lead to errors and unexpected behaviors.

So, what exactly is a default export in JavaScript? A default export is used to export a single object, function, or a class that is intended to be the primary functionality provided by a module. When another module imports from this module, it can directly import the default export without the need for curly braces or specifying a name.

The syntax for exporting a default object looks like this:

export default objectName;

Now, let's delve into why having multiple default exports in a single module is not permitted. When you define a default export in a module, it becomes the primary export of that module. If you attempt to add another default export in the same module, JavaScript doesn't know how to handle the ambiguity of having multiple primary exports. This confusion results in a syntax error, preventing the module from being loaded correctly.

To illustrate, consider the following example where we have a module named `myModule.js`:

export default function myFunction() {
   // Function implementation
}

export default class myClass {
   // Class implementation
}

In this scenario, the second `export default` statement for the class `myClass` would throw a syntax error. To overcome this limitation, you can either convert one of the default exports to a named export or create a wrapper object to hold multiple exports. Let's see how you can resolve this issue.

To convert one of the default exports to a named export, modify the module as follows:

export default function myFunction() {
   // Function implementation
}

export class myClass {
   // Class implementation
}

By changing the second `export default` to `export class`, you now have a default export (the function `myFunction`) and a named export (the class `myClass`) within the module, resolving the conflict.

Alternatively, you can create a wrapper object to encompass multiple exports:

const moduleExports = {
   myFunction: function() {
      // Function implementation
   },
   myClass: class {
      // Class implementation
   }
};

export default moduleExports;

In this setup, the `moduleExports` object contains both the function and the class, and then this object is exported as the default export of the module. When importing from this module, you can access the individual exports through the `moduleExports` object.

Understanding the limitation of having multiple default exports in a module is essential for avoiding syntax errors and ensuring a smooth workflow when working with JavaScript modules. By following the suggested approaches, you can structure your modules effectively and prevent issues related to conflicting default exports.

Remember, keeping your code organized and following best practices will not only enhance the readability of your code but also make it easier for you and other developers to maintain and collaborate on projects.