混合mixin

两个对象，混合后产生一个新对象

es6之前的写法

function maxin(obj1,obj2){
            var newObj = {};
            for(var key in obj2){
                newObj[key] = obj2[key];
            }
            for(var key in obj1){
                if(!(key in obj2)){
                    newObj[key] = obj1[key];
                }
            }
            return newObj;
        }

es6之后

Object.assign({}, obj1, obj2);