Copyright Jörn Zaefferer; licensed MIT

plugin.js

var rocambole = require('rocambole');
var _tk = require('rocambole-token');

var MAX_LINE_LENGTH = 75;

exports.transformAfter = function(ast) {
  rocambole.recursive(ast, transform);
};

function transform(node) {
  if (node.type !== 'ObjectExpression') return;

  // Don't collapse nested objects
  if (node.parent.type === 'Property') return;

  // It collapses objects that are short enough
  // 0 indicates measurement failed, ignore
  var length = expectedLength(node);
  if (length === 0 || length > MAX_LINE_LENGTH) return;

  // This one seems short
  _tk.eachInBetween(node.startToken, node.endToken, function(token) {
    if (_tk.isBr(token)) {

      // Insert one blank to replace the line break
      _tk.before(token, {
        type: 'WhiteSpace',
        value: ' '
      });

      // Remove all whitespace/indent after the line break
      var next = token.next;
      while (_tk.isEmpty(next)) {
        _tk.remove(next);
        next = next.next;
      }

      // Remove the line break itself
      _tk.remove(token);
    }
  });
}

function expectedLength(node) {
  var length = 0;

  var startOfTheLine = _tk.findPrev(node.startToken, 'LineBreak');

  // No linebreak indicates first line of the file, find first token instead
  if (!startOfTheLine) {
    startOfTheLine = _tk.findPrev(node.startToken, function(token) {
      return !token.prev;
    });
  }
  var firstChar = _tk.findNextNonEmpty(startOfTheLine);

  // Need to take into consideration the indent
  _tk.eachInBetween(startOfTheLine, firstChar, function(token) {
    length += String(token.raw || token.value).length;
  });

  var prev;
  _tk.eachInBetween(firstChar, node.endToken, function(token) {
    if (_tk.isEmpty(token)) {

      // Empty tokens are "collapsed" (multiple linebreaks/whitespace becomes
      // a single whitespace)
      length += _tk.isEmpty(prev) ? 0 : 1;
      prev = token;
      return;
    }

    // Don't collapse objects with line comments; block comments should be okay
    if (token.type === 'LineComment') {
      length += 1000;
    }
    length += String(token.raw || token.value).length;
    prev = token;
  });

  if (length === 0) {
    throw new Error('Failed to measure length of object expression: ' + node.toString());
  }

  return length;
}