The Object.defineProperties()
method defines new or modifies existing properties directly on an object, returning the object.
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Syntax
Object.defineProperties(obj, props)
Parameters
obj
- The object on which to define or modify properties.
props
- An object whose keys represent the names of properties to be defined or modified and whose values are objects describing those properties. Each value in
props
must be either a data descriptor or an accessor descriptor; it cannot be both (seeObject.defineProperty()
for more details). - Data descriptors and accessor descriptors may optionally contain 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.
Defaults tofalse
.enumerable
true
if and only if this property shows up during enumeration of the properties on the corresponding object.
Defaults tofalse
.
A data descriptor also has the following optional keys:
value
- The value associated with the property. Can be any valid JavaScript value (number, object, function, etc).
Defaults toundefined
. writable
true
if and only if the value associated with the property may be changed with an assignment operator.
Defaults tofalse
.
An accessor descriptor also has the following optional keys:
get
- A function which serves as a getter for the property, or
undefined
if there is no getter. The function's return value will be used as the value of the property.
Defaults toundefined
. set
- A function which serves as a setter for the property, or
undefined
if there is no setter. The function will receive as its only argument the new value being assigned to the property.
Defaults toundefined
.
If a descriptor has neither of
value
,writable
,get
andset
keys, it is treated as a data descriptor. If a descriptor has bothvalue
orwritable
andget
orset
keys, an exception is thrown.
Return value
The object that was passed to the function.
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; }
Examples
Using Object.defineProperties
var obj = {}; Object.defineProperties(obj, { 'property1': { value: true, writable: true }, 'property2': { value: 'Hello', writable: false } // etc. etc. });
Specifications
Specification |
---|
ECMAScript (ECMA-262) The definition of 'Object.defineProperties' in that specification. |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
defineProperties | Chrome Full support 5 | Edge Full support 12 | Firefox Full support 4 | IE Full support 9 | Opera Full support 11.6 | Safari Full support 5 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 12 | Safari iOS Full support 5 | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
Legend
- Full support
- Full support