Web/JavaScript/Reference/Global objects/Object/ defineSetter

This feature is deprecated in favor of defining setters using the object initializer syntax or the Object.defineProperty() API.

However, as it is widely implemented and used on the Web, it is very unlikely that browsers will stop implementing it.

The __defineSetter__ method binds an object's property to a function to be called when an attempt is made to set that property.

Syntax

obj.__defineSetter__(prop, fun)

Parameters

prop

A string containing the name of the property to be bound to the given function.

fun

A function to be called when there is an attempt to set the specified property. This function takes the form

function(val) { . . . }

val: An alias for the variable that holds the value attempted to be assigned to prop.

Return value

undefined.

Description

The __defineSetter__ method allows a setter to be defined on a pre-existing object.

Examples

Non-standard and deprecated way

var o = {};
o.__defineSetter__('value', function(val) { this.anotherValue = val; });
o.value = 5;
console.log(o.value); // undefined
console.log(o.anotherValue); // 5

Standard-compliant ways

// Using the set operator
var o = { set value(val) { this.anotherValue = val; } };
o.value = 5;
console.log(o.value); // undefined
console.log(o.anotherValue); // 5

// Using Object.defineProperty
var o = {};
Object.defineProperty(o, 'value', {
  set: function(val) {
    this.anotherValue = val;
  }
});
o.value = 5;
console.log(o.value); // undefined
console.log(o.anotherValue); // 5

Specifications

Specification
ECMAScript (ECMA-262)The definition of 'Object.prototype.__defineSetter__()' in that specification.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
`__defineSetter__` Deprecated'	Chrome Full support 1	Edge Full support 12	Firefox Full support 1 Notes' Full support 1 Notes' Notes' Starting with Firefox 48, this method can no longer be called at the global scope without any object. A `TypeError` will be thrown otherwise. Previously, the global object was used in these cases automatically, but this is no longer the case.	IE Full support 11	Opera Full support 9.5	Safari Full support 3	WebView Android Full support 1	Chrome Android Full support 18	Firefox Android Full support 4	Opera Android Full support 10.1	Safari iOS Full support 1	Samsung Internet Android Full support 1.0	nodejs Full support Yes

Legend

Full support: Full support
Deprecated. Not for use in new websites.': Deprecated. Not for use in new websites.
See implementation notes.': See implementation notes.