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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	Status	Comment
ECMAScript Latest Draft (ECMA-262) The definition of 'Object.prototype.__defineSetter__()' in that specification.	Draft	Included in the (normative) annex for additional ECMAScript legacy features for Web browsers (note that the specification codifies what is already in implementations).

Browser compatibilityUpdate compatibility data on GitHub

	Desktop
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari
Basic support	Yes	Yes	1 1 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.	11	Yes	Yes

	Mobile
	Android webview	Chrome for Android	Edge Mobile	Firefox for Android	Opera for Android	iOS Safari	Samsung Internet
Basic support	Yes	Yes	Yes	4	Yes	Yes	Yes

	Server
	Node.js
Basic support	Yes

object.__defineSetter__