Object.prototype.__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

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See also