Compare lines indentation detection

compare.js

function detectIndent(lines) {
  var indents = {}; // # spaces indent -> # times seen
  var last = 0;     // # leading spaces in the last line we saw

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

    var indent = Math.abs(width - last);
    if (indent > 1) {
      indents[indent] = (indents[indent] || 0) + 1;
    }
    last = width;
  });

  // find most frequent non-zero width difference
  var indent = null, max = 0;
  for (var width in indents) {
    width = parseInt(width, 10);
    var tally = indents[width];
    if (tally > max) {
      max = tally;
      indent = width;
    }
  }

  return indent;
}