小编Roh*_*bre的帖子

我在集合列表中有以下记录

db.ilists.find()

{ "_id" : ObjectId("5efb10f25372d01d549954b1"), "name" : "hello user", "__v" : 0 }
{ "_id" : ObjectId("5efb10f25372d01d549954b2"), "name" : "click + to add items to the list", "__v" : 0 }
{ "_id" : ObjectId("5efb10f25372d01d549954b3"), "name" : "<---click the checkbox to deletet item in the list", "__v" : 0 }
{ "_id" : ObjectId("5efb170a32b1290c64950999"), "__v" : 0 }
{ "_id" : ObjectId("5efb17790d9ff700204c43c2"), "__v" : 0 }

我有两个空文档，我正在使用 deleteMany 删除它们，但我得到以下信息

> db.ilists.deleteMany({"_id":"5efb170a32b1290c64950999"},{"_id":"5efb17790d9ff700204c43c2"})
{ "acknowledged" : true, "deletedCount" : 0 } …

我在这里对可变提升概念有点困惑。为什么第一个console.log(flag)输出undefined？它不应该捕获已经初始化的 false 值在作用域链中向上移动吗？

var flag = false;
(function(){
    console.log(flag);
    var flag = true; // JavaScript only hoists declarations, not initialisations

    console.log(flag);

    if(flag){
        let name = "John";
        const age = "24";

        console.log(name);
        console.log(age);
    }

    //console.log(name); //ReferenceError: name is not defined ( as name is block scoped here )
    //console.log(age);  //ReferenceError: age is not defined ( as age is block scoped )

})();