normalizeLineEndings

Normalizes line endings in a string.

Use String.prototype.replace() and a regular expression to match and replace line endings with the normalized version. Omit the seconds argument, normalized, to use the default value of '\r\n'.

const normalizeLineEndings = (str, normalized = "\r\n") =>
  str.replace(/\r?\n/g, normalized);

splitLines("This\r\nis a\nmultiline\nstring.\r\n"); // 'This\r\nis a\r\nmultiline\r\nstring.\r\n'
splitLines("This\r\nis a\nmultiline\nstring.\r\n", "\n"); // 'This\nis a\nmultiline\nstring.\n'