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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
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 2017 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 compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | 11 | (Yes) | (Yes) |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | (Yes) | ? | (Yes) | (Yes) |
Compatibility notes
- Starting with Firefox 48 (Firefox 48 / Thunderbird 48 / SeaMonkey 2.45), 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 (bug 1253016).
See also
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