javascript - About the isPlainObject function in jQuery source code to determine whether the object is a pure object-PHP Chinese Network Q&A

// 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

Why the output isfalse
Object.hasOwnProperty.call(proto, "constructor") && proto.constructor;What does it mean
Object.hasOwnProperty.toString.call( Object )The output isfunction Object() { [native code] }
Object.hasOwnProperty. toString.call(Number)The output isfunction Number() { [native code] }why

// 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; }

reply all (1)

巴扎黑2017-06-12 09:30:36 1 floor

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.