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  3. Node.js — Check if a Path is a File URL

Node.js — Check if a Path is a File URL

Node.js includes the needed functionality to interact with files on your local hard disk. Typically, you’re referencing files on disk using a file path. This path can have different formats, like a relative or an absolute path or a file URL.

With the transition to ECMAScript modules developers are going to interact with file URLs. The reason for that: modules are loaded via file URLs, like import './my-module.js'.

This tutorial shows you how to detect whether a given path is a file: URL. We’re also creating a helper function detecting whether a given path (as a string value) represents a file: URL.

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Determine Whether a Path Points to a File URL

When interacting with files you may think of using the Node.js node:fs core module. Yet, thenode:fs module won’t help here because we’re going to interact with URLs and need to find another way. We can’t use the fs.stats() method either, because file: URLs represent paths on the disk and there’s no file-specific information we need.

Instead, we need to take one step back and should use the Node.js global URL class (that implements the WHATWG URL standard). The URL class is helpful to determine whether a given input maps to a file: URL.

Here’s the isFileUrl utility method that you can use in your projects. Inputs 

/**
 * Determine whether the given `path` is a `file:` URL. This method
 * accepts a string value and a URL instance. You may adjust the
 * allowed parameters if you don’t want to support both types.
 *
 * @param {String|URL} path
 *
 * @returns {Boolean}
 */
function isFileUrl(path) {  
  // `path` is neither a string nor a URL -> early return
  if (typeof path !== 'string' && !(path instanceof URL)) {
    return false
  }

  try {
    const url = new URL(path)

    return url.protocol === 'file:'
  } catch (error) {
    return false
  }
}

isFileUrl(import.meta.resolve('.'))  
isFileUrl('file:///home/users/marcus')  
isFileUrl(new URL('file:///home/users/marcus'))  
// true

isFileUrl(null)  
isFileUrl('/home/users/marcus')  
// false

We have related tutorials here on Future Studio to this tutorial. You might be interested in one of the following articles:

Enjoy!

Mentioned Resources

Marcus Pöhls

Marcus is a fullstack JS developer. He’s passionate about the hapi framework for Node.js and loves to build web apps and APIs. Creator of Futureflix and the “learn hapi” learning path.

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