GCD indentation detection

gcd.js

function detectIndent(lines) {
  var widths = [];

  lines.forEach(function (text) {
    var width = leadingSpaces(text);

    // throw out odd numbers so comments don't throw us
    if (width % 2 == 1) {
      return;
    }
    widths.push(width);
  });

  // now get the largest width that divides all of them
  var indent = widths.reduce(gcd);
  return indent;
}

/* Greatest common divisor of two numbers */
function gcd(n, m) {
  return m > 0 ? gcd(m, n % m) : n;
}