Sample code to upload files via API is listed below. Assumes http://localhost:8080/ as the base URL for the API calls.

Upload local file

let axios = require("axios").default;
let FormData = require('form-data');
let fs = require('fs');

// Configurations
//
const project_id = '<Project Identifier>';
const table_id = '<Table Identifier>';
const xc_token = '<Auth Token>';
const file_path = '<Local File Path>';


// Insert Image
// @param image_path : local file path
// @return : JSON object to be used in insert record API for attachment field
//
async function insertImage (path) {
    const formData = new FormData();
    formData.append("file", fs.createReadStream(path));
    const data = await axios({
        url: 'http://localhost:8080/api/v2/storage/upload',
        data: formData,
        headers:{
            'Content-Type':`multipart/form-data;`,
            'xc-token': xc_token
        },
        method: 'post',

        // Optional : storage file path
        params: {"path": "somePath"}
    });
    return data;
}

// Insert record with attachment
// Assumes a table with two columns :
//      'Title' of type SingleLineText and
//      'Attachment' of type Attachment
//
async function uploadFileExample() {
    let response = await insertImage(file_path);

    let row = {
        "Title": "2",
        "Attachment": response.data
    };

    await axios({
        method: 'POST',
        url: `http://localhost:8080/api/v2/tables/${table_id}/records`,
        data: row,
        headers: {
            'xc-token': xc_token
        }
    });
}

(async () => {
    await uploadFileExample();
})();

Upload via URL

let axios = require("axios").default;
let FormData = require('form-data');
let fs = require('fs');

// Configurations
//
const project_id = '<Project Identifier>';
const table_id = '<Table Identifier>';
const xc_token = '<Auth Token>';

// URL array : URLs of files to be uploaded
const URLs = [{ url: '<URL1>' }, { url: '<URL2>' }];

// Insert Image
// @param URLs : [] containing public URL for files to be uploaded
// @return : JSON object to be used in insert record API for attachment field
//
async function insertImageByURL (URL_array) {
    const data = await axios({
        url: 'http://localhost:8080/api/v2/storage/upload-by-url',
        data: URL_array,
        headers: {
            'xc-token': xc_token
        },
        method: 'post',

        // Optional : storage file path
        params: {"path": "somePath"}
    });
    return data;
}

// Insert record with attachment
// Assumes a table with two columns :
//      'Title' of type SingleLineText and
//      'Attachment' of type Attachment
//
async function uploadByUrlExample() {
    let response = await insertImageByURL(URLs);

    // Update two columns : Title and Attachment
    let row = {
        "Title": "3",
        "Attachment": response.data
    };

    await axios({
        method: 'POST',
        url: `http://localhost:8080/api/v2/tables/${table_id}/records`,
        data: row,
        headers: {
            'xc-token': xc-token
        }
    });
}

(async () => {
    await uploadByUrlExample();
})();