Object.defineProperties()
Object.defineProperties()
函式可定義新的或是修改已存在的物件屬性,並回傳修改後的物件。
語法
Object.defineProperties(obj, props)
參數
obj
-
The object on which to define or modify properties.
props
-
An object whose own enumerable properties constitute descriptors for the properties to be defined or modified. Property descriptors present in objects come in two main flavors: data descriptors and accessor descriptors (see
Object.defineProperty()
for more details). Descriptors have the following keys:configurable
-
true
if and only if the type of this property descriptor may be changed and if the property may be deleted from the corresponding object. 預設為false
. enumerable
-
若該屬性設為 true,則該屬性可被物件所列舉。
預設為false
. value
-
The value associated with the property. Can be any valid JavaScript value (number, object, function, etc). 預設為
undefined
. writable
-
若該屬性為 true
,則該屬性可透過賦予運算子 (en-US)所改變 預設為false
. get
-
A function which serves as a getter for the property, or
undefined
if there is no getter. The function return will be used as the value of property. 預設為undefined
. set
-
A function which serves as a setter for the property, or
undefined
if there is no setter. The function will receive as only argument the new value being assigned to the property. 預設為undefined
.
回傳值
The object that was passed to the function.
描述
Object.defineProperties
, in essence, defines all properties corresponding to the enumerable own properties of props
on the object obj
object.
範例
var obj = {};
Object.defineProperties(obj, {
'property1': {
value: true,
writable: true
},
'property2': {
value: 'Hello',
writable: false
}
// etc. etc.
});
Polyfill
Assuming a pristine execution environment with all names and properties referring to their initial values, Object.defineProperties
is almost completely equivalent (note the comment in isCallable
) to the following reimplementation in JavaScript:
function defineProperties(obj, properties) {
function convertToDescriptor(desc) {
function hasProperty(obj, prop) {
return Object.prototype.hasOwnProperty.call(obj, prop);
}
function isCallable(v) {
// NB: modify as necessary if other values than functions are callable.
return typeof v === 'function';
}
if (typeof desc !== 'object' || desc === null)
throw new TypeError('bad desc');
var d = {};
if (hasProperty(desc, 'enumerable'))
d.enumerable = !!desc.enumerable;
if (hasProperty(desc, 'configurable'))
d.configurable = !!desc.configurable;
if (hasProperty(desc, 'value'))
d.value = desc.value;
if (hasProperty(desc, 'writable'))
d.writable = !!desc.writable;
if (hasProperty(desc, 'get')) {
var g = desc.get;
if (!isCallable(g) && typeof g !== 'undefined')
throw new TypeError('bad get');
d.get = g;
}
if (hasProperty(desc, 'set')) {
var s = desc.set;
if (!isCallable(s) && typeof s !== 'undefined')
throw new TypeError('bad set');
d.set = s;
}
if (('get' in d || 'set' in d) && ('value' in d || 'writable' in d))
throw new TypeError('identity-confused descriptor');
return d;
}
if (typeof obj !== 'object' || obj === null)
throw new TypeError('bad obj');
properties = Object(properties);
var keys = Object.keys(properties);
var descs = [];
for (var i = 0; i < keys.length; i++)
descs.push([keys[i], convertToDescriptor(properties[keys[i]])]);
for (var i = 0; i < descs.length; i++)
Object.defineProperty(obj, descs[i][0], descs[i][1]);
return obj;
}
規範
Specification |
---|
ECMAScript Language Specification # sec-object.defineproperties |
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