How to use local file as thumbnail in DiscordJS em

Question

Is it possible to use a local file as a thumbnail for an embedded message with DiscordJs?

"thumbnail": {
  "url": "../img/025.png"
},

This doesn't seem to work.

(node:34721) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1):  
DiscordAPIError: Invalid Form Body 
embed.thumbnail.url: Not a well formed URL.

Normal URL's do work however.

Answer 1

I've already found an answer. Linking to the proper url of the file wasn't an option for me, because some images were generated.

You can attach an image to the message, and use this attachment as thumbnail. Most basic example:

const embed = {
  "title": "A Title" ,
  "color": 0xF96221,
  "thumbnail": {
    "url": "attachment://image.png"
  },
  "fields": [
    {
      "name": "Field 1:",
      "value": "One",
      "inline": false
    },
    {
      "name": "Field 2:",
      "value": "Two",
      "inline": true,
    },
    {
      "name":"Field 3:",
      "value":"Three",
      "inline": true
    },
  ],
  "footer": {
    "text":"Footer text"
  }
};

Attach the image to the message with:

message.channel.send({
  embed,
  files: [{
    attachment:'img/image.png',
    name:'image.png'
  }]
});