get-file-object-from-local-path

Create a JS File object instance from a local path

Usage no npm install needed!

<script type="module">
  import getFileObjectFromLocalPath from 'https://cdn.skypack.dev/get-file-object-from-local-path';
</script>

README

get-file-object-from-local-path

A utility to get a JS file object from a local file system path, when using Node together with a frontend client.

This solves the lack of interoperability between Node's fs file system (which the browser doesn't have access to), and the browser's File object type, which Node cannot create.

Install

This is a Node.js module available through the npm registry. Installation is done using the npm install command:

$ npm install get-file-object-from-local-path

How to use

The utility contains two functions:

  1. LocalFileData(): an object constructor function that takes an absolute path as an argument

Call this within a Node environment, passing an absolute path as a single argument, to construct a LocalFileData object containing all the data required to construct a file object in the frontend client:

  • name: the name of the original file
  • arrayBuffer: an arrayBuffer created using the buffer of the original file
  • type: a MIME type based on the extension of the source file. Returns undefined if it can't be deduced.
// Within node.js
const fileData = new LocalFileData('path/to/file.txt')
  1. constructFileFromLocalFileData(): a function to convert the provided LocalFileData object into a JS File object. This must be executed in the frontend code, which has access to the window.File constructor.
// Within browser code
const file = constructFileFromLocalFileData(fileData) // returns a JS File object

Once created, this file behaves the same way as a JS File object created using an HTML file picker, for example.

Use cases

get-file-object-from-local-path was created to specify files to process and then send from the main thread to the renderer thread in Electron; however, a LocalFileData instance is a plain object that can be serialized/stringified and transmitted in any way required.

Example workflow:

  1. Client sends the path of a file to the Node.js environment
  2. Backend retrieves file, processes it and creates a LocalFileData object of the result
  3. Node.js environment sends LocalFileData object to client
  4. Client converts LocalFileData object to a File object for e.g. upload to server

Limitations

Please note that although any file can be converted into a LocalFileData object, the entire file is loaded into memory when serializing (which will be required as a general rule when sending using Electron's ipcRenderer or as an http request).

Files of >1GB will therefore cause the process to crash if serialization is required. This package is intended for transmitting smaller pieces of data and is not suitable for e.g. large videos.

License

MIT