code: function mergeInto(one, two) {
    checkMergeObjectArg(one);
    if (two != null) {
      checkMergeObjectArg(two);
      for (var key in two) {
        if (!two.hasOwnProperty(key)) {
          continue;
        }
        one[key] = two[key];
      }
    }
  }
docs: Shallow merges two structures by mutating the first parameter.
  
  @param {object} one Object to be merged into.
  @param {?object} two Optional object with properties to merge from.