Readline interface

Part 2

Node.js's native readline module can be applied in various situations for reading some sort of stream line-by-line, e.g. with a TCP socket or with a file stream to quickly make a cat command:

// cat.js
#!/usr/bin/env node
import { createInterface } from 'readline';
import * as fs from 'fs';
import * as path from 'path';

const fileStream = createReadStream(resolve(process.argv[2]), 'utf8');

createInterface(fileStream, process.stdout);

A less trivial example for using the readline interface with files would be reading a large file line-by-line to do processing while buffering very little of the file directly into memory:

const doSomethingLineByLine = async () => {
  const rl = createInterface(createReadStream('path/to/file', 'utf8'));

  for await (const line of rl) {
    doSomething(line);
  }
};