hasOwnProperty(), propertyIsEnumerable() and isPrototypeOf() in JS

First understand the enum properties

Generally, use for~in traversal

 var a = [1,2,3];for(var i in a){console.log(a[i]);}orvar o = {p1:1,p2:2};for(var i in o){console.log(i+'='+o[i]);}//p1=1;p2=2;

<1> Not all attributes will be displayed in the for~in traversal. For example (array) length attribute and constructor attribute. Those properties that have been displayed are called enumerables, and the properties that are enumerables can be determined by the propertyIsEnumerable() method provided by each object;

<2> Each attribute in the prototype chain will also be displayed, provided that they are enumerable, hasOwnProperty() to determine whether a property is an object's own property or a prototype property;

<3> For all prototype properties, propertyIsEnumerable() will return false, including those enumerable in the for ~in traversal.

js code example

 function dog(name,color){this.name = name;this.color = color;this.someMethod = function(){return 1;}}dog.prototype.price=100;dog.prototype.rating=3;var newDog = new dog("doggg","yellow");for(var prop in newDog){console.log(prop+'='+newDog[prop]);}//name=doggg//color=yellow//someMethod=function (){return 1;}//price=100//rating=3newDog.hasOwnProperty('name');//true;newDog.hasOwnProperty('price');//false;

Show only its own attributes

 for(var prop in newDog){if(newDog.hasOwnProperty(prop )){console.log(prop+'='+newDog[prop]);}}newDog.propertyIsEnumerable('name');//truenewDog.propertyIsEnumerable('constructor');//false

Note: Most of the built-in properties and methods are not enumerable.

Any attributes from the prototype chain are also not enumerable

If the call to propertyIsEnumerable() is from an object on the prototype chain, then the properties in that object are enumerable

 newDog.constructor.prototype.propertyIsEnumerable('price');//true

isPrototypeOf(): Each object has it, indicating whether the current object is a prototype of another object

js code example

 var monkey = {hair:true,feeds:'bananas',breathes:'air'};function Human(name){this.name = name;}Human.prototype = monkey;var george = new Human('George');monkey.isPrototypeOf(george);//true

The above is the hasOwnProperty(), propertyIsEnumerable() and isPrototypeOf() in JS introduced to you by the editor. I hope it will be helpful to everyone. If you have any questions, please leave me a message and the editor will reply to everyone in time. Thank you very much for your support to Wulin.com website!