count lines in nodejs

index.js

//@ts-check

async function main() {
  const assert = require('assert');
  (/**@type {[number, string][]}*/([
    [0, ''],
    [1, ' '],
    [1, '1'],
    [1, '\n'],
    [1, '\r'],
    [1, '\r\n'],
    [1, '1'],
    [1, '1\n'],
    [1, '1\r'],
    [1, '1\r\n'],
    [2, '\n\n'],
    [2, '\r\r'],
    [2, '\n\r'],
    [2, '1\n2'],
    [2, '1\n2\n'],
    [2, '1\n '],
    [4, '1\n2\r3\r\n4'],
  ])).forEach(async ([expected, text]) => {
    assert.strictEqual(expected, countLinesSync(text));
    assert.strictEqual(expected, await countLines(text));
  });

  /**
   * @param {string} text 
   * @returns {Promise<number>}
   */
  async function countLines(text) {
    if (!text || text.length === 0) {
      return 0;
    }

    const readline = require('node:readline');
    const stream = require('node:stream');

    const textStream = new stream.Readable();
    textStream.push(text);
    textStream.push(null);

    const rl = readline.createInterface({
      input: textStream
    });

    let count = 0;
    for await (const _ of rl) {
      count += 1;
    }

    rl.close();
    textStream.destroy();

    return count;
  }

  /**
   * @param {string} text 
   * @returns {number}
   */
  function countLinesSync(text) {
    const LF = '\n';
    const CR = '\r';

    const textLengh = text?.length || 0;
    let lineCount = 0;
    let feedNewLine = true;
    for (let i = 0; i < textLengh; i++) {
      const char = text[i];

      if (feedNewLine) {
        lineCount++;
        feedNewLine = false;
      }

      if (char === LF || char === CR) {
        /*CRLF*/
        if (char === CR && i < textLengh && text[i + 1] === LF)
          i++;
        feedNewLine = true;
      }
    }

    return lineCount;
  }
}

main();