var fs = require('fs').promises; function genFile() { let content = '000010000112022030S2300420300001AWM001000604' let thisFile = '' for(let i = 30000; i <= 100000; i++) { if(i%200 == 0 || i == 30000) { thisFile = getFileName(i) console.log(thisFile) } if(i == 100000) { console.log("9999" + paddy(i,6) + content); continue } console.log("99999" + paddy(i,5) + content); } } function getFileName(i) { if(i+200 == 100000) { return "99999" + paddy(i+1,5) + "-" + paddy(i+200,6) + ".inv" } return "99999" + paddy(i+1,5) + "-" + paddy(i+200,5) + ".inv" } function paddy(num, padlen, padchar) { var pad_char = typeof padchar !== 'undefined' ? padchar : '0'; var pad = new Array(1 + padlen).join(pad_char); return (pad + num).slice(-pad.length); } genFile()