Search string in file NodeJS - using streams

search-stream.js

const fs = require('fs');
const readline = require('readline');
const stream = require('stream');

const searchStream = (filename, text) => {

    return new Promise((resolve) => {
        const inStream = fs.createReadStream('file/' + filename + ".txt");
        const outStream = new stream;
        const rl = readline.createInterface(inStream, outStream);
        const result = [];
        const regEx = new RegExp(text, "i")
        rl.on('line', function (line) {
            if (line && line.search(regEx) >= 0) {
                result.push(line)
            }
        });
        rl.on('close', function () {
            console.log('finished search', filename)
            resolve(result)
        });
    })
}

Related to article https://medium.com/codex/achieve-the-best-performance-search-a-string-in-file-using-nodejs-6a0f2a3b6cfa