Obsolete
This feature is obsolete. Although it may still work in some browsers, its use is discouraged since it could be removed at any time. Try to avoid using it.
The __noSuchMethod__
property used to reference a function to be executed when a non-existent method is called on an object, but this function is no longer available.
While __noSuchMethod__
has been dropped, the ECMAScript 2015 (ES6) specification has the Proxy
object, with which you can achieve the below (and more).
Syntax
obj.__noSuchMethod__ = fun
Parameters
fun
- A function that takes the form
-
function (id, args) { . . . }
id
- The name of the non-existent method that was called
args
- An array of the arguments passed to the method
Description
By default, an attempt to call a method that doesn't exist on an object results in a TypeError
being thrown. This behavior can be circumvented by defining a function at that object's __noSuchMethod__
member. The function takes two arguments, the first is the name of the method attempted and the second is an array of the arguments that were passed in the method call. The second argument is an actual array (that is, it inherits through the Array.prototype
chain) and not the array-like arguments object.
If this method cannot be called, either as if undefined
by default, if deleted, or if manually set to a non-function, the JavaScript engine will revert to throwing TypeError
s.
Examples
Simple test of __noSuchMethod__
var o = { __noSuchMethod__: function(id, args) { console.log(id, '(' + args.join(', ') + ')'); } }; o.foo(1, 2, 3); o.bar(4, 5); o.baz(); // Output // foo (1, 2, 3) // bar (4, 5) // baz ()
Using __noSuchMethod__
to simulate multiple inheritance
An example of code that implements a primitive form of multiple inheritance is shown below.
// Doesn't work with multiple inheritance objects as parents function noMethod(name, args) { var parents = this.__parents_; // Go through all parents for (var i = 0; i < parents.length; i++) { // If we find a function on the parent, we call it if (typeof parents[i][name] == "function") { return parents[i][name].apply(this, args); } } // If we get here, the method hasn't been found throw new TypeError; } // Used to add a parent for multiple inheritance function addParent(obj, parent) { // If the object isn't initialized, initialize it if (!obj.__parents_) { obj.__parents_ = []; obj.__noSuchMethod__ = noMethod; } // Add the parent obj.__parents_.push(parent); }
An example of using this idea is shown below.
// Example base class 1 function NamedThing(name){ this.name=name; } NamedThing.prototype = { getName: function() { return this.name; }, setName: function(newName) { this.name = newName; } } // Example base class 2 function AgedThing(age) { this.age = age; } AgedThing.prototype = { getAge: function() { return this.age; }, setAge: function(age) { this.age = age; } } // Child class. inherits from NamedThing and AgedThing // as well as defining address function Person(name, age, address){ addParent(this, NamedThing.prototype); NamedThing.call(this, name); addParent(this, AgedThing.prototype); AgedThing.call(this, age); this.address = address; } Person.prototype = { getAddr: function() { return this.address; }, setAddr: function(addr) { this.address = addr; } } var bob = new Person("bob", 25, "New York"); console.log("getAge is " + (("getAge" in bob) ? "in" : "not in") + " bob"); // getAge is not in bob console.log("bob's age is: " + bob.getAge()); // bob's age is: 25 console.log("getName is " + (("getName" in bob) ? "in" : "not in") + " bob"); // getName is not in bob console.log("bob's name is: " + bob.getName()); // bob's name is: bob console.log("getAddr is " + (("getAddr" in bob) ? "in" : "not in") + " bob"); // getAddr is in bob console.log("bob's address is: " + bob.getAddr()); // bob's address is: New York
Specifications
Not part of any specifications. This feature has been removed, see bug 683218.
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | No support | No support [1] | No support | No support | No support |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | No support | No support | No support [1] | No support | No support | No support |
[1] This feature was implemented until version 43.