How to count raw characters in a string in javascript?

OK, I've tried to answer in the comment but it wasn't pleasant to read.

The issue is split in two major problems:

• counting raw chars
• counting ASCII length instead of UTF-16 one

I will answer to both issues with examples.

counting raw chars

The only way to consider '\n' string as two chars with one backslash and one n letter, is to use a function tag and a template literal.

const rawlength = tpl => tpl.raw.join('').length;

`a\nb`.length;   // 3
rawlength`a\nb`; // 4

You can copy and paste above code and read the two different results. Bear in mind, not using parenthesis with rawlength is not a typo, but how template literals work.

Also bear in mind if you use a template literal like the following one

`a
b`

its length will still be 3 because there is indeed no backslash in there, so the \n char is considered one char as it should be.

In Python, that would be equivalent

len("""a
b""")

That' a 3.

Edit: the Python r in JavaScript

The equivalent of r in JavaScript would be:

const r = (t, ...v) => {
  const result = [t.raw[0]];
  const length = t.length;
  for (let i = 1; i < length; i++)
    result.push(v[i - 1], t.raw[i]);
  return result.join('');
};

So that:

r`a\nb`

Would produce what you expect.

You can add the following trick around result.join('') to also have the length as ASCII/bytes instead.

counting ASCII length instead of UTF-16 one

This is an old trick to always count bytes:

unescape(encodeURIComponent('a“b')).length;

That's a 5, because encodeURIComponent would return an UTF-8 url friendly version of the text, and unescape will create a char per each %XX encountered.

In this case 'a“b' becomes a%E2%80%9Cb which is ab plus 3 url encoded chars.