code: function mergeIntoWithNoDuplicateKeys(one, two) {
    ("production" !== "development" ? invariant(
      one && two && typeof one === 'object' && typeof two === 'object',
      'mergeIntoWithNoDuplicateKeys(): Cannot merge non-objects.'
    ) : invariant(one && two && typeof one === 'object' && typeof two === 'object'));
  
    for (var key in two) {
      if (two.hasOwnProperty(key)) {
        ("production" !== "development" ? invariant(
          one[key] === undefined,
          'mergeIntoWithNoDuplicateKeys(): ' +
          'Tried to merge two objects with the same key: `%s`. This conflict ' +
          'may be due to a mixin; in particular, this may be caused by two ' +
          'getInitialState() or getDefaultProps() methods returning objects ' +
          'with clashing keys.',
          key
        ) : invariant(one[key] === undefined));
        one[key] = two[key];
      }
    }
    return one;
  }
docs: Merge two objects, but throw if both contain the same key.
  
  @param {object} one The first object, which is mutated.
  @param {object} two The second object
  @return {object} one after it has been mutated to contain everything in two.