readline.js

// Read line by line from a file.
const fs = require('fs');
const readline = require('readline');
const stream = require('stream')

function processFile(inputFile) {
  const instream = fs.createReadStream(inputFile);
  const outstream = new (stream)();
  const rl = readline.createInterface(instream, outstream);
     
    rl.on('line', function (line) {
        console.log(line);
    });
    
    rl.on('close', function (line) {
        console.log(line);
        console.log('done reading file.');
    });
}
processFile('/path/to/a/input/file.txt');

//////////////////////////////////////////////////////////////////////

// Read the entire file in utf8 format.

fs.readFile('input.txt', 'utf8', function (err, data) {
  if (err) throw err;
  console.log(data);
});