Let me sort out your code. To be honest, I don’t like your coding style very much, because all kinds of unnecessary variable declarations lead to poor code expression

First of all I assume you are using express because you use req.body

//这个定义是为了什么？是为了防止你老板炒了你所以把代码写的别人看不懂吗？
//var _q = req.body, _qId = mongoose.Types.ObjectId(_q["_id"]);

groups.findById(req.body._id, function (err, docById) {
    if(err){
        res.json({code: 404, msg: "Error"});
    }else{
        groups.findOne({name:req.body.name}, null)
            .exec(function (_err, docByName) {
               console.log(docById._id == docByName._id);
            });
    }
});

That is to say, two values ​​are passed in your post request, one is _id and the other is name. You use the two values ​​​​to search the database respectively, so you get two search results (two doc), and then you try to compare whether the doc obtained through _id search and the doc searched through name are the same thing (of course comparing _id is to compare whether they are the same doc)

Based on the conditions you gave, I first guessed whether the _id and name in the req.body you gave match. Maybe they come from two different docs? Or maybe there are two docs with the same name in your database, so the doc obtained through name search and the doc obtained through id search are not the same?

You can try to print docById and docByName before the final console.log, and post your mongoose scheme to take a look. This way we at least know what kind of database you are searching for

 groups.findOne({name:_q["name"]},null).exec(function (_err,_data) {
            console.log(data["_id"] == _data["_id"]);
        });

This uses findOne, which will only return one record. Maybe there are multiple values ​​with the same name in the library, and the one you took out happens to be different from the one you want

The method has been found: convert the _id obtained in Step 1 using String().

Full code

var _q = req.body, _qId = mongoose.Types.ObjectId(_q["_id"]);

groups.findById(_qId,function (err,data) {
    if(err){
        res.json({code: 404, msg: "Error"});
    }else{
        groups.findOne({name:_q["name"]},null).exec(function (_err,_data) {
            console.log(String(data["_id"]) == _data["_id"]);
        });
    }
});