No of Lines of Code in A Function

• Lesser the lines of code, the easier it is to read and understand.
  • A nice descriptive name and 1 line of code, that's the best function we can write.
  • Why write 1 line of code into a separate function? Well, to give it a descriptive name and so that it can be reused if needed.
• But of course not all functions can be 1 liners. But on the other hand, too big function becomes much harder to read. So we should have a limit: 10 lines max in a function

The authentication example from avoiding nested if checks is around 11 lines, it can still be broken down into smaller pieces as follows:

DO NOT split like this 💩💩💩

/**
 * While it might be tempting to split it like this,
 * It's actually hard to understand what's going on 💩
 */

function isTokenEmpty(token) {
  // nothing to do if the auth header doesn't exist
  if (!token) return 401;

  const headerParts = token.split(' ');
  if (headerParts.length !== 2) return 401; // header value is wrong

  const bearerToken = headerParts[1];
  if (bearerToken === '') return 401; // empty token
}

function authenticate(req, res, next) {
  // nothing to do if authModule isn't ready for some reason.
  if (!authModule.initialized) throw new Error('Auth Module is not initialized');

  // this function doesn't return anything, so we don't know what it does,
  // We're forced to open and look into this function to understand what it does! 💩
  isTokenEmpty(req.headers['Authentication']);

  try {
    const payload = authModule.validateToken(req.headers['Authentication'].split(' ')[1]);
    return payload;
  } catch (err) {
    return 401;
  }
}

Instead do like this ✅

function sanitizeToken(token) {
  // nothing to do if the auth header doesn't exist
  if (!token) return '';

  const headerParts = token.split(' ');
  if (headerParts.length !== 2) return ''; // header value is wrong

  const bearerToken = headerParts[1];
  if (bearerToken === '') return ''; // empty token

  return bearerToken;
}

function authenticate(req, res, next) {
  // nothing to do if authModule isn't ready for some reason.
  if (!authModule.initialized) throw new Error('Auth Module is not initialized');

  // We don't need to open the following function,
  // unless we're really interested to see how it sanitizes the token ✅
  const token = sanitizeToken(req.headers['Authentication']);
  if (token === '') return 401;

  try {
    const payload = authModule.validateToken(token);
    return payload;
  } catch (err) {
    return 401;
  }
}