Began to use mongo to find a problem, which is difficult to describe. please look at the code slowly.

  mongodb, 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
}

Question 1

var d = t

Is it a reference assignment? If so, how about not using a reference assignment?

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

Question 2: I will execute it.

delete d.password

Returns true to indicate that it has been deleted, why should I execute it again

d.password=124

Two additions are performed

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

At first contact is not very clear, hope to know the reason

First question … because the two entries are the sameObjectIdTherefore, it is regarded as the same article. …

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

The second question cannot be reproduced, so I do not know …

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