Object.defineProperties()

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

Browser compatibility

Based on Kangax's compat tables.

See also

• Object.defineProperty()
• Object.keys()
• Enumerability and ownership of properties