Table of contents
1. Add attributes or methods to an object, generally do this
2. Use Object.defineproperty to add properties or methods
2. Comparison of methods for obtaining the key of an object
5.Object.getOwnPropertySymbols
1. Preliminary summary
Let’s take a look at Object.defineproperty first.
Object.defineproperty is to directly define a new property on an object, or modify an existing property.
1. Add attributes or methods to an object, generally do this
let params = {};
//新增name属性
params.name="CSDN";
//新增userAction方法
params.userAction=function() {
console.log("这是新添加的方法");
};
console.log(parmas);
//结果打印{name: 'CSDN', userAction: ƒ}2. Use Object.defineproperty to add properties or methods
Object.defineproperty（obj, prop, desc ）
Parameter 1: obj The current object whose properties need to be defined
Parameter 2: prop The name of the property that currently needs to be defined
Parameter 3: desc descriptor is generally an object
let params = {};
Object.defineProperty(params,'name',{
value:'CSDN'
});
Object.defineProperty(params,'userAction',{
value:function() {
console.log("这是新添加的方法");
}
});
//其它属性如下，此处不做分析
//writable：是否可重写
//value：当前值
//get：读取时内部调用的函数
//set：写入时内部调用的函数
//enumerable：是否可枚举
//configurable：是否可再次修改配置项2. Comparison of methods for obtaining the key of an object
We define two objects parent and children.
Defined in parent:
parentName: enumerable property
parentAge: non-enumerable property
parentSex attribute
parent's symbol attribute
//定义parent对象
let parent = {};
Object.defineProperty(parent,'parentName',{
value:'这是parentName',
enumerable:true,//可枚举
});
Object.defineProperty(parent,'parentAge',{
value:'这是parentAge',
enumerable:false,//不可枚举
});
Object.defineProperty(parent,'parentSex',{
value:Symbol("男性"),
enumerable:true,
});
let parentIdCard = Symbol('身份证号');
parent[parentIdCard] = parentIdCard;
console.log(parent);
parent prints the results:
defined in childeren:
childrenName: enumerable property
childrenAge: non-enumerable property
childrenSex property
symbol attribute of children
//定义children对象
let children = {};
Object.defineProperty(children,'childrenName',{
value:'这是childrenName',
enumerable:true,//可枚举
});
Object.defineProperty(children,'childrenName',{
value:'这是childrenName',
enumerable:false,//不可枚举
});
Object.defineProperty(children,'childrenSex',{
value:Symbol("男性"),
enumerable:true,
});
let childrenIdCard = Symbol('身份证号');
children[childrenIdCard] = childrenIdCard;
console.log(children);
children.__proto__ = parent;
children print results:
children inherit parent;
1.for in
for(let p in children) {
console.log(p);
}
The result is as follows:
It can be seen that for in traverses all enumerable properties of itself and inheritance; it does not include non-enumerable and Symbol properties.
2.Object.keys
console.log(Object.keys(children));
The result is as follows:
It can be seen that Object.keys will return an array after execution, and only traverses its own enumerable properties; excluding non-enumerable and Symbol properties
3.Object.getOwnPropertyNames
console.log(Object.getOwnPropertyNames(children));
The result is as follows:
It can be seen that Object.getOwnPropertyNames returns an array after execution, traversing its own enumerable properties and non-enumerable properties; it does not include the Symbol property
4.Reflect.ownKeys
console.log(Reflect.ownKeys(children));
It can be seen that Reflect.ownKeys returns an array after execution, traversing all its own attributes, including enumerable, non-enumerable, and Symbol attributes.
5.Object.getOwnPropertySymbols
console.log(Object.getOwnPropertySymbols(children));
The result is as follows:
It can be seen that Object.getOwnPropertySymbols returns an array after execution, traversing all the Symbol properties of the object itself
Summarize
for in: Traverse all its own and inherited enumerable properties. Excludes non-enumerable properties and Symbol properties
Object.keys(): Returns an array; gets its own (without inheritance) enumerable properties. Excludes non-enumerable properties and Symbol properties
Object.getOwnPropertyNames: Returns an array; gets all its own (excluding inheritance) property names, including non-enumerable properties, excluding Symbol properties
Object.getOwnPropertySymbols: Returns an array that traverses all Symbol properties of the object itself
Reflect.ownKeys: Returns an array; obtains all property names of itself (excluding inheritance), including non-enumerable properties and Symbol. In fact, it is the sum of Object.getOwnPropertyNames and Object.getOwnPropertySymbols
Only for in contains inherited enumerable properties;
Only Object.getOwnPropertySymbols and Reflect.ownKeys can contain Symbol properties;
Only Object.getOwnPropertyNames and Reflect.ownKeys contain non-enumerable properties;