CouchDB update handler for partial updates of a document.

partial-update.js

function (doc, req) {
  var findTheChanges = function (prevK, obj) {
    var arr = [];
    for (var key in obj) {
      var prevKey = prevK || '';
      if (obj.hasOwnProperty(key)) {
        var value = obj[key];
        // If its an Object dig deeper.
        if (value !== null &&
            typeof value === 'object' &&
            value.constructor !== Array) {
          prevKey += key;
          prevKey += ',';
          var deepArr = findTheChanges(prevKey, value);
          arr = arr.concat(deepArr);
        }
        // Found the value to affect.
        else {
          arr.push({
            path: prevKey + key,
            value: value
          });
        }
      }
    }

    return arr;
  };

  if (!doc) {
    return [null, JSON.stringify({
      doc: req.id,
      status: 'nodoc'
    })];
  }

  var _obj = JSON.parse(req.body);
  var arrayOfChanges = findTheChanges(null, _obj);
  for (var i = 0, len1 = arrayOfChanges.length; i < len1; i++) {
    var path = (arrayOfChanges[i].path).split(',');
    var value = arrayOfChanges[i].value;
    var newDoc = doc;
    for (var j = 0, len2 = path.length; j < len2; j++) {
      // If it's not the final value, and niether is an Object,
      // it should be an empty Object to build the new chain.
      if (j + 1 < len2 &&
          (typeof newDoc[path[j]] !== 'object' ||
           newDoc[path[j]].constructor === Array ||
           newDoc[path[j]] === null)) {
        newDoc[path[j]] = {};
      }
      if (j + 1 === len2) newDoc[path[j]] = value;
      else newDoc = newDoc[path[j]];
    }
  }

  return [doc, JSON.stringify({
    doc: req.id,
    status: 'updated'
  })];
}