mongodb - 开始使用mongo 发现一个问题，很难描述，请慢慢看代码

Question

 db.mongo.insert({name:'mongo'});
> var t=db.mongo.findOne();
> t
{ "_id" : ObjectId("5141b98723616e67f947f356"), "name" : "mongo" }
> var d=t   
> d
{ "_id" : ObjectId("5141b98723616e67f947f356"), "name" : "mongo" }
> d.password=123
123
> d
{
	"_id" : ObjectId("5141b98723616e67f947f356"),
	"name" : "mongo",
	"password" : 123
}
> t
{
	"_id" : ObjectId("5141b98723616e67f947f356"),
	"name" : "mongo",
	"password" : 123
}

问题1

var d = t

是引用赋值吗 如果是的话，怎么样不使用引用赋值

delete d.password
true
> d
{ "_id" : ObjectId("5141b98723616e67f947f356"), "name" : "mongo" }
> d.password=124
124
> d
{
	"_id" : ObjectId("5141b98723616e67f947f356"),
	"name" : "mongo",
	"password" : 124,
	"password" : 124
}

问题2 我执行

delete d.password

返回 true 说明已经删除，为什么我再执行

d.password=124

会执行两次添加

> d
{
	"_id" : ObjectId("5141b98723616e67f947f356"),
	"name" : "mongo",
	"password" : 124,
	"password" : 124
}

刚开始接触 不是很明白，希望有知道的说明下原因

Answer 1

The first question... Because the two entries have the same ObjectId, they are regarded as the same one...

Although it is not actually a reference assignment, you can understand it this way...

The second problem cannot be reproduced, so I don’t know...

Answer 2

This is either the same problem with ObjectId, or simply JavaScript syntax requires reference assignment. If you want to clone, watch this. http://stackoverflow.com/questions/122102/most-efficient-way-to-clone-an-object

I haven’t encountered the second problem either.

Answer 3

Yes, this is purely a Javascript syntax issue. This problem exists in Javascript. That is, the problem of deep copy and shallow copy:

var cloneObj = function(obj){
    var str, newobj = obj.constructor === Array ? [] : {};
    if(typeof obj !== 'object'){
        return;
    } else if(window.JSON){
        str = JSON.stringify(obj), //系列化对象
        newobj = JSON.parse(str); //还原
    } else {
        for(var i in obj){
            newobj[i] = typeof obj[i] === 'object' ? 
            cloneObj(obj[i]) : obj[i]; 
        }
    }
    return newobj;
};

Code transferred from https://www.zhihu.com/question/23031215