readLines(): stream a file with readline

import { createReadStream } from 'node:fs';
import { createInterface } from 'node:readline';

/** Stream a text file lazily; huge logs never load into memory at once. */
export async function* readLines(path: string): AsyncGenerator<string, void, void> {
  const stream = createReadStream(path, { encoding: 'utf8' });
  const lines = createInterface({ input: stream, crlfDelay: Infinity });
  try {
    for await (const line of lines) yield line;
  } finally {
    lines.close();
    stream.destroy();
  }
}

/** Read only the first `limit` lines, closing the stream early. */
export async function readFirstLines(path: string, limit = 20): Promise<string[]> {
  const selected: string[] = [];
  if (limit <= 0) return selected;
  for await (const line of readLines(path)) {
    selected.push(line);
    if (selected.length >= limit) break;
  }
  return selected;
}

// for await (const line of readLines('./access.log')) console.log(line);