你什么时候使用Object.defineProperty() [英] when do you use Object.defineProperty()
问题描述
我想知道何时应该使用
Object.defineProperty
为对象创建新属性。我知道我可以设置类似
to create new properties for an object. I'm aware that I'm able to set things like
enumerable: false
但你什么时候需要这个呢?如果你只是设置一个属性,如
but when do you need this really? If you just set a property like
myObject.myprop = 5;
它的描述符都设置为true,对吧?当你们使用相当冗长的.defineProperty()调用以及出于什么原因时,我实际上更好奇。
its descriptors are all set to true, right? I'm actually more curious when you guys use that rather verbose call to .defineProperty() and for what reasons.
推荐答案
< a href =https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Object/defineProperty> Object.defineProperty
主要用于设置具有特定属性描述符的属性(例如只读(常量),可枚举性(不显示 for(.. in ..)
loop,getters,setters)。
Object.defineProperty
is mainly used to set properties with specific property descriptors (e.g. read-only (constants), enumerability (to not show a property in a for (.. in ..)
loop, getters, setters).
"use strict";
var myObj = {}; // Create object
// Set property (+descriptor)
Object.defineProperty(myObj, 'myprop', {
value: 5,
writable: false
});
console.log(myObj.myprop);// 5
myObj.myprop = 1; // In strict mode: TypeError: myObj.myprop is read-only
示例
此方法使用属性扩展 Object
原型。仅定义了getter,并且可枚举性设置为 false
。
Example
This method extends the Object
prototype with a property. Only the getter is defined, and the enumerability is set to false
.
Object.defineProperty(Object.prototype, '__CLASS__', {
get: function() {
return Object.prototype.toString.call(this);
},
enumerable: false // = Default
});
Object.keys({}); // []
console.log([].__CLASS__); // "[object Array]"
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