query {
  boards (ids:1234567890) {
    items (limit:100) {
      assets {
        id
        url
        name
      }
    }
  }
}

fetch ("https://api.monday.com/v2", {
  method: 'post',
  headers: {
    'Content-Type': 'application/json',
    'Authorization' : 'YOUR_API_KEY_HERE'
   },
   body: JSON.stringify({
     query : "query { boards (ids: 1234567890) { items (limit: 100) { assets { id url name }}";
   })
  });

mutation {
	add_file_to_update (update_id: 1234567890, file: YOUR_FILE) {
		id
	}
}

/// those are the main dependecies you'll need to have installed in this example;
const fs = require('fs');
const fetch = require('node-fetch');

/// Replace with your actual API Key
const API_KEY= "YOUR_API_KEY_HERE";

/// Notice the /file/ endpoint - only this endpoint will support variables in this type of call
const url = 'https://api.monday.com/v2/file';

/// This is your mutation query - can also be adapted to send files to file columns instead
const query = 'mutation ($file: File!) { add_file_to_update (update_id: 1234567890, file: $file) {id}}'

///This is the mapping for the API call, where you specify that a variable should be considered as the variables[file] of the request. 
///This can be called "image", or simply file - as long as it matches the name of the multipart request later down the line.
var map = {"image":"variables.file"};

/// this is the path to the file you'd like to upload to monday.com
var upfile  = `./300px-All_Right_Then,_Keep_Your_Secrets.jpg`;

var data = "";
const boundary = "xxxxxxxxxxxxxxx";

fs.readFile(upfile, function(err, content){

    // simple catch error
    if(err){
        console.error(err);
    }

    //below, we will construct a multipart request. Take a look at the "name" within each part, as those will refer to different parts of the API call.

    // construct query part
    data += "--" + boundary + "\r\n";
    data += "Content-Disposition: form-data; name=\"query\"; \r\n";
    data += "Content-Type:application/json\r\n\r\n";
    data += "\r\n" + query + "\r\n";

    // construct map part
    data += "--" + boundary + "\r\n";
    data += "Content-Disposition: form-data; name=\"map\"; \r\n";
    data += "Content-Type:application/json\r\n\r\n";
    data += "\r\n" + JSON.stringify(map)+ "\r\n";

    // construct file part - the name needs to be the same as passed in the map part of the request. So if your map is {"image":"variables.file"}, the name should be image.
    data += "--" + boundary + "\r\n";
    data += "Content-Disposition: form-data; name=\"image\"; filename=\"" + upfile + "\"\r\n";
    data += "Content-Type:application/octet-stream\r\n\r\n";
    var payload = Buffer.concat([
            Buffer.from(data, "utf8"),
            new Buffer.from(content, 'binary'),
            Buffer.from("\r\n--" + boundary + "--\r\n", "utf8"),
    ]);

    // construct request options
    var options = {
        method: 'post',
        headers: {
          "Content-Type": "multipart/form-data; boundary=" + boundary,
          "Authorization" : API_KEY
        },
        body: payload,
    };

    // make request
    fetch(url, options)
      .then(res => res.json())
      .then(json => console.log(json));
});

mutation {
	add_file_to_column (item_id: 1234567890, column_id: "files", file: YOUR_FILE) {
		id
	}
}

var fs = require('fs');
var fetch = require('node-fetch'); // requires node-fetch as dependency

// adapted from: https://gist.github.com/tanaikech/40c9284e91d209356395b43022ffc5cc

// set filename
var upfile = 'sample.png';

// set auth token and query
var API_KEY = "MY_API_KEY"
var query = 'mutation ($file: File!) { add_file_to_column (file: $file, item_id: 1234567890, column_id: "files") { id } }';

// set URL and boundary
var url = "https://api.monday.com/v2/file";
var boundary = "xxxxxxxxxx";
var data = "";

fs.readFile(upfile, function(err, content){

    // simple catch error
    if(err){
        console.error(err);
    }

    // construct query part
    data += "--" + boundary + "\r\n";
    data += "Content-Disposition: form-data; name=\"query\"; \r\n";
    data += "Content-Type:application/json\r\n\r\n";
    data += "\r\n" + query + "\r\n";

    // construct file part
    data += "--" + boundary + "\r\n";
    data += "Content-Disposition: form-data; name=\"variables[file]\"; filename=\"" + upfile + "\"\r\n";
    data += "Content-Type:application/octet-stream\r\n\r\n";
    var payload = Buffer.concat([
            Buffer.from(data, "utf8"),
            new Buffer.from(content, 'binary'),
            Buffer.from("\r\n--" + boundary + "--\r\n", "utf8"),
    ]);

    // construct request options
    var options = {
        method: 'post',
        headers: {
          "Content-Type": "multipart/form-data; boundary=" + boundary,
          "Authorization" : API_KEY
        },
        body: payload,
    };

    // make request
    fetch(url, options)
      .then(res => res.json())
      .then(json => console.log(json));
});