compare-structure.js

var hasOwn = Object.prototype.hasOwnProperty;
var indexOf = Array.prototype.indexOf;

function isObjectEmpty(obj) {
  for (var key in obj) {
    return false;
  }

  return true;
}

function copyKeys(obj) {
  var newObj = {};

  for (var key in obj) {
    newObj[key] = undefined;
  }

  return newObj;
}

// compares the structure of JSON-compatible, non-circular values
function compareStructure(a, b) {
  if (typeof a !== typeof b) {
    return false;
  }

  if (typeof a === 'object') {
    // both or neither, but not mismatched
    if (Array.isArray(a) !== Array.isArray(b)) {
      return false;
    }

    if (Array.isArray(a)) {
      // can't compare structure in array if we don't have items in both
      if (!a.length || !b.length) {
        return true;
      }

      for (var i = 1; i < a.length; i++) {
        if (!compareStructure(a[0], a[i])) {
          return false;
        }
      }

      for (var i = 0; i < b.length; i++) {
        if (!compareStructure(a[0], b[i])) {
          return false;
        }
      }

      return true;
    }

    var map = copyKeys(a), keys = Object.keys(b);

    for (var i = 0; i < keys.length; i++) {
      var key = keys[i];

      if (!hasOwn.call(map, key) || !compareStructure(a[key], b[key])) {
        return false;
      }

      delete map[key];
    }

    // we should've found all the keys in the map
    return isObjectEmpty(map);
  }

  return true;
}