javascript - About the isPlainObject function in jQuery source code to determine whether the object is a pure object

Question

// Objects with prototype are plain iff they were constructed by a global Object function
Ctor = hasOwn.call( proto, "constructor" ) && proto.constructor; //这行是什么意思？
return typeof Ctor === "function" && fnToString.call( Ctor ) === ObjectFunctionString;

The following are the codes mentioned in the appeal code

var class2type = {};
var toString = class2type.toString;
var getProto = Object.getPrototypeOf;
var hasOwn = class2type.hasOwnProperty;
var fnToString = hasOwn.toString; 
var ObjectFunctionString = fnToString.call( Object );
var proto, Ctor;
proto = getProto( obj );

In jQuery 3.2.1, the last two lines of the function that determines whether an object is a pure object are not equivalent when I tested it myself. I would like to ask what the problem is

var obj = function(){};
var proto = Object.getPrototypeOf(obj);
var Ctor = Object.hasOwnProperty.call(proto, "constructor") && proto.constructor;
var objHasOwn = Object.hasOwnProperty.toString.call( Object );
var funcHasOwn = Object.hasOwnProperty.toString.call( Ctor );

console.log(funcHasOwn === objHasOwn); // 我使用纯 function 来测试，发现结果是 false

Ask me

1. Why the output is false

2. Object.hasOwnProperty.call(proto, "constructor") && proto.constructor; What does it mean

3. Object.hasOwnProperty.toString.call( Object ) The output is function Object() { [native code] }
Object.hasOwnProperty. toString.call(Number)The output isfunction Number() { [native code] } why

Answer 1

    // 判断参数是不是纯粹的对象 通过{}、new Object()、Object.create(null)
    isPlainObject: function( obj ) {
        var proto, Ctor;

        // 借用toString方法判断obj的类型是不是Object
        if ( !obj || toString.call( obj ) !== "[object Object]" ) {
            return false;
        }
        // 获取对象的原型
        proto = getProto( obj );

        // 通过Object.create( null )创建的对象返回true
        if ( !proto ) {
            return true;
        }

        // 判断对象是不是通过new Object()方式创建的
        Ctor = hasOwn.call( proto, "constructor" ) && proto.constructor;
        // fnToString：将函数转换成字符串 ObjectFunctionString：function Object() { [native code] }
        return typeof Ctor === "function" && fnToString.call( Ctor ) === ObjectFunctionString;
    }

1. var obj = function(){}; returns false because you have misunderstood the function of this function. It does not mean to create it through a function, it means new Object();

Object.hasOwnProperty.toString.call(Number) output is function Number() { [native code] } because Object.hasOwnProperty.toString will return the object's constructor function in string form, and the call method borrows from Object.hasOwnProperty toString method.