React Native: How to create excel file from code?

If using Expo, the following code should work for you. It creates a Sheet and then creates a Share dialog for the user to open it in which ever app they like like Email, Office, etc:

import XLSX from 'xlsx';
import * as FileSystem from 'expo-file-system';
import * as Sharing from 'expo-sharing';

var data = [{
    "name": "John",
    "city": "Seattle"
  },
  {
    "name": "Mike",
    "city": "Los Angeles"
  },
  {
    "name": "Zach",
    "city": "New York"
  }
];
var ws = XLSX.utils.json_to_sheet(data);
var wb = XLSX.utils.book_new();
XLSX.utils.book_append_sheet(wb, ws, "Cities");
const wbout = XLSX.write(wb, {
  type: 'base64',
  bookType: "xlsx"
});
const uri = FileSystem.cacheDirectory + 'cities.xlsx';
console.log(`Writing to ${JSON.stringify(uri)} with text: ${wbout}`);
await FileSystem.writeAsStringAsync(uri, wbout, {
  encoding: FileSystem.EncodingType.Base64
});

await Sharing.shareAsync(uri, {
  mimeType: 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet',
  dialogTitle: 'MyWater data',
  UTI: 'com.microsoft.excel.xlsx'
});

You can convert JSON to excel file

You have to use two pacakge

1. react-native-fs
2. XLSX (for convert json to excel file)

here is an example

if you want to write Excel file

import { writeFile, readFile } from 'react-native-fs';
import XLSX from 'xlsx';

var data = [
{"name":"John", "city": "Seattle"},
{"name":"Mike", "city": "Los Angeles"},
{"name":"Zach", "city": "New York"}
];

 var ws = XLSX.utils.json_to_sheet(data);

  var wb = XLSX.utils.book_new();
  XLSX.utils.book_append_sheet(wb,ws,"Prova");

  const wbout = XLSX.write(wb, {type:'binary', bookType:"xlsx"});
  var RNFS = require('react-native-fs');
  var file = RNFS.ExternalStorageDirectoryPath + '/test.xlsx';
  writeFile(file, wbout, 'ascii').then((r)=>{/* :) */}).catch((e)=>{/* :( */});

if you want to read Excel file

import { writeFile, readFile } from 'react-native-fs';
import XLSX from 'xlsx';

  const filePath="/Users/copoo/Downloads/Data.xlsx";
  const excelFile=await RNFS.readFile(filePath,'ascii');
  const workbook = XLSX.read(excelFile, {type:'binary'});
  console.log(workbook,"excelFile")

I would use JSON, which is native to JavaScript, and can be imported directly into Excel

If you don't already know how, Here is a post explaining how to create a JSON file from a JS object:

write/add data in JSON file using node.js