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;
}
規格
Specification | Status | 註記 |
---|---|---|
ECMAScript 5.1 (ECMA-262) The definition of 'Object.defineProperties' in that specification. |
Standard | Initial definition. Implemented in JavaScript 1.8.5 |
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Object.defineProperties' in that specification. |
Standard | |
ECMAScript Latest Draft (ECMA-262) The definition of 'Object.defineProperties' in that specification. |
Draft |
瀏覽器相容性
We're converting our compatibility data into a machine-readable JSON format.
This compatibility table still uses the old format,
because we haven't yet converted the data it contains.
Find out how you can help!
Feature | Firefox (Gecko) | Chrome | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | 4.0 (2) | 5 | 9 | 11.60 | 5 |
Feature | Firefox Mobile (Gecko) | Android | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|
Basic support | 4.0 (2) | (Yes) | ? | 11.5 | (Yes) |