src/deps/extend.js

import clone from './clone';

function extendInner(obj, otherObj) {
  for (var key in otherObj) {
    if (otherObj.hasOwnProperty(key)) {
      var value = clone(otherObj[key]);
      if (typeof value !== 'undefined') {
        obj[key] = value;
      }
    }
  }
}

function extend(obj, obj2, obj3) {
  extendInner(obj, obj2);
  if (obj3) {
    extendInner(obj, obj3);
  }
  return obj;
}

export default extend;