split-lines.mjs

//========== .split() with lookbehind ==========
// Downside: Safari doesn’t support lookbehind

import * as assert from 'node:assert/strict';

const RE_SPLIT_AFTER_EOL = /(?<=\r?\n)/;
function splitLinesWithEols1(str) {
  return str.split(RE_SPLIT_AFTER_EOL);
}

assert.deepEqual(
  splitLinesWithEols1('there\nare\r\nmultiple\nlines'),
  ['there\n', 'are\r\n', 'multiple\n', 'lines']
);
assert.deepEqual(
  splitLinesWithEols1('first\n\nthird'),
  ['first\n', '\n', 'third']
);
assert.deepEqual(
  splitLinesWithEols1('EOL at the end\n'),
  ['EOL at the end\n']
);
assert.deepEqual(
  splitLinesWithEols1('\r\n'),
  ['\r\n']
);
assert.deepEqual(
  splitLinesWithEols1(''),
  ['']
);

//========== .indexOf() ==========

import * as assert from 'node:assert/strict';

function splitLinesWithEols2(str) {
  if (str.length === 0) return [''];
  const lines = [];
  let prevEnd = 0;
  while (prevEnd < str.length) {
    const newlineIndex = str.indexOf('\n', prevEnd);
    // If there is a newline, it’s included in the line
    const end = newlineIndex < 0 ? str.length : newlineIndex+1;
    lines.push(str.slice(prevEnd, end));
    prevEnd = end;
  }
  return lines;
}

assert.deepEqual(
  splitLinesWithEols2('there\nare\r\nmultiple\nlines'),
  ['there\n', 'are\r\n', 'multiple\n', 'lines']
);
assert.deepEqual(
  splitLinesWithEols2('first\n\nthird'),
  ['first\n', '\n', 'third']
);
assert.deepEqual(
  splitLinesWithEols2('EOL at the end\n'),
  ['EOL at the end\n']
);
assert.deepEqual(
  splitLinesWithEols2('\r\n'),
  ['\r\n']
);
assert.deepEqual(
  splitLinesWithEols2(''),
  ['']
);