Error in delete trigger function when using dependency import.

Michael_Rojkov · 2025-04-15T06:04:18.792Z

I want to use a combination of TTL and delete Triggers, to delete items in a second database.

Every item in my collection has a link to a corresponding image, that is stored in a vercel blob storage.
If the Item is deleted from my collection, I want to delete the corresponding image in the blob.

To do this, I set up a function in a delete trigger, that uses the image link, to delete the image.

Here is the code I used:

exports = async function(changeEvent) {
  try {
    // Import the Vercel Blob SDK
    const { del } = require('@vercel/blob');
    
    // Get the full document before it was deleted
    const deletedDoc = changeEvent.fullDocumentBeforeChange;
    
    if (!deletedDoc || !deletedDoc['flyerUrl']) {
      console.log('No flyer image found in deleted document');
      return;
    }
    
    const flyerUrl = deletedDoc['flyerUrl'];
    console.log(`Attempting to delete flyer image: ${flyerUrl}`);
    
    // Set up Vercel Blob configuration
    // These values should be stored as secrets in your MongoDB Atlas environment
    const config = {
      token: context.values.get("VERCEL_BLOB_TOKEN")
    };
    
    // Delete the blob directly
    await del(flyerUrl, config);
    console.log(`Successfully deleted blob: ${flyerUrl}`);
    
  } catch (error) {
    console.error("Error in delete trigger function:", error.message);
  }

The VERCEL_BLOB_TOKEN was saved as a secret for MongoDB to access.

Since this code requires the vercel/blob API, I used the “add Dependancy” function to include @vercel/blob

vercel.com

@vercel/blob

Learn how to use the Vercel Blob SDK to access your blob store from your apps.

I was shown that the import was successful.

When running the function, I was prompted an error:

Error in delete trigger function: failed to compile source for module '@vercel/blob': SyntaxError: node_modules/@vercel/blob/dist/index.cjs: Line 35:7 Unexpected token function (and 30 more errors)
> result: 
{
   "$undefined": true
}
> result (JavaScript): 
EJSON.parse('{"$undefined":true}')

From this point on, I am unsure what to do. Did the import not work correctly, or is this a problem with the @vercel/blob api?

Does anyone have experience with this and can point me in the right direction?

Paolo_Manna · 2025-04-15T06:57:55.517Z

Hi @Michael_Rojkov,

The main issue here seems to be that the @vercel/blob isn’t supported: as explained in the docs

Atlas App Services automatically transpiles dependencies and also supports most built-in Node.js modules.

Thus, here it seems that this transpiling step failed: this isn’t uncommon, the App Services Function engine is partially compatible with Node.js v10, so possibly a previous version of the package may work, but this isn’t guaranteed either, as there are some unsupported features.

As an aside, about the line

      token: context.values.get("VERCEL_BLOB_TOKEN")

Please note that you cannot read a Secret directly, you need to access it via a linked value.