Detecting whether an ES module is run from the command line in Node.js can be achieved through various approaches. Let's explore a few common methods:
Using import.meta
The import.meta
object provides information about the current module. It includes a url
property that contains the URL of the module. You can compare this URL with the current script's file path to determine if the module is being run directly or imported:
if (import.meta.url === `file://${process.argv[1]}`) {
// module was not imported but called directly
}
```
Note that you may need to use path.resolve()
or path.normalize()
to ensure that the file path comparison is accurate across different platforms.
Using module Global Variable
In CommonJS modules, the module
global variable is defined. However, in ES modules, this variable is not available. You can leverage this difference to detect the module type:
const inCommonJs = typeof module !== 'undefined';
console.log(`inCommonJs = ${inCommonJs}`);
```
This approach is straightforward and works in both CommonJS and ES modules.
Using require.main
The require.main
property points to the module that was the direct entry point for the Node.js process. If the module is being run as the main script, require.main
will be equal to the current module:
if (require.main === module) {
// module was executed directly
}
```
This method is particularly useful when dealing with CLI scripts that are executed directly from the command line.
Using pathToFileURL
The pathToFileURL()
function can be used to convert a file path to a file URL. This can be helpful for comparing the module URL with the current script's file path:
import { pathToFileURL } from 'url';
if (import.meta.url === pathToFileURL(process.argv[1]).href) {
// module was not imported but called directly
}
```
This approach is particularly useful when dealing with Windows paths, where backslashes need to be handled correctly.
Using realpathSync and pathToFileURL
This approach combines the realpathSync()
function from the fs
module with pathToFileURL()
to resolve symlinks and convert the file path to a file URL:
import { realpathSync } from "fs";
import { pathToFileURL } from "url";
function wasCalledAsScript() {
// Resolve symlinks
const realPath = realpathSync(process.argv[1]);
// Convert file path to file URL
const realPathAsUrl = pathToFileURL(realPath).href;
return import.meta.url === realPathAsUrl;
}
if (wasCalledAsScript()) {
// module was executed and not imported by another file
}
```
This approach is particularly useful for handling CLI scripts that are executed from symlinked paths.
The choice of approach depends on your specific requirements and preferences. Consider factors such as compatibility with different Node.js versions and the specific use case you're targeting.