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    Object.prototype.__noSuchMethod__

    Obsolete since Gecko 39 (Firefox 39 / Thunderbird 39 / SeaMonkey 2.36)
    This feature is obsolete.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.

    Non-standard
    This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.

    While __noSuchMethod__ is non-standard, the ECMAScript Harmony (ES6) specification will have Proxy, with which you can achieve the below (and more).
     

    Summary

    The __noSuchMethod__ property references a function to be executed when a non-existent method is called on an object.

    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 TypeErrors.

    Examples

    Example: 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 ()
    

    Example: 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");
    console.log("bob's age is: " + bob.getAge());
    console.log("getName is " + (("getName" in bob) ? "in" : "not in") + " bob");
    console.log("bob's name is: " + bob.getName());
    console.log("getAddr is " + (("getAddr" in bob) ? "in" : "not in") + " bob");
    console.log("bob's address is: " + bob.getAddr());
    

    Example output would be follows:

    getAge is not in bob
    bob's age is: 25
    getName is not in bob
    bob's name is: bob
    getAddr is in bob
    bob's address is: New York
    

    Specifications

    Not part of any specifications.

    Browser compatibility

    Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
    Basic support Not supported 1.0 (1.7 or earlier) Not supported Not supported Not supported
    Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
    Basic support Not supported Not supported 1.0 (1.0) Not supported Not supported Not supported

     This feature is going to be removed in the future, see bug 683218.

    Document Tags and Contributors

    Last updated by: fscholz,