defineProperties Redirect 1

Summary

The Object.defineProperties() method defines new or modifies existing properties directly on an object, returning the object.

Syntax

Object.defineProperties(obj, props)

Parameters

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.

Description

Object.defineProperties, in essence, defines all properties corresponding to the enumerable own properties of props on the object objrops object.

Example

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 = !!obj.enumerable;
    if (hasProperty(desc, "configurable"))
      d.configurable = !!obj.configurable;
    if (hasProperty(desc, "value"))
      d.value = obj.value;
    if (hasProperty(desc, "writable"))
      d.writable = !!desc.writable;
    if ( hasProperty(desc, "get") ) {
      var g = desc.get;

      if (!isCallable(g) && g !== "undefined")
        throw new TypeError("bad get");
      d.get = g;
    }
    if ( hasProperty(desc, "set") ) {
      var s = desc.set;
      if (!isCallable(s) && 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;
}

Specifications

Specification Status Comment
ECMAScript Language Specification 5.1th Edition (ECMA-262) Standard Initial definition.
Implemented in JavaScript 1.8.5
ECMAScript Language Specification 6th Edition (ECMA-262) Draft  

Browser compatibility

Based on Kangax's compat tables.

Feature Firefox (Gecko) Chrome Internet Explorer Opera Safari
Basic support 4.0 (2) 5 (previous versions untested) 9 11.60 5
Feature Firefox Mobile (Gecko) Android IE Mobile Opera Mobile Safari Mobile
Basic support 4.0 (2) (Yes) ? 11.50 (Yes)

See also

Document Tags and Contributors

Contributors to this page: Sheppy
Last updated by: Sheppy,