>> Here’s one simple way to do it in Javascript (using extjs here):

JavaScript’s language design already supports [Trait] implementation
mechanics in its most native way via [Function] objects and its two
caller methods [apply] or [call].

A trait gets written like any constructor function. Your given example
code than will turn into:

var MyTrait = (function () {

this.xhr = (function (config) {
return Ext.Ajax.request(config);
});
this.submit = (function (basic_form,config) {
// perform some checks on config
// and call basic_form.submit
});
// … add more utility functions
});

The JavaScript code for applying such behavior onto already existing
instances of whatever kind (var obj = new SomeVeryComplexObjectModel;)
literaly states what it does:

MyTrait.call(obj);

And it is simple as well to make this kind of subtyping (is it allowed
calling it *interface inheritance*?) part of a constructor function:

var SomeVeryComplexObjectModel = (function () {

MyTrait.call(this); // applying or mixing in the [MyTrait] type

/*
defining the objects constructing [SomeVeryComplexObjectModel] type
*/
});

How about that defenition of mine, I came up with a while ago, cause
I wanted to make understood myself the languages different approches
and wordings of what I’d like to call Traits in JavaScript too.

»The concept of “Mixin”s from the perspective of
JavaScript adds behavior to objects by delegation
over implemented interfaces. “Trait”s might be
the wording that comes closest to this languages
design.
Furthermore, “augment” describes far better the
mechanism behind this special kind of interface
inheritance than “mix in” does.«

Pleace correct me. If it comes to the basic principles of computer
science I’m merely an interested layman.

so long – peterS.

var MyGrid = Ext.extend(Ext.grid.GridPanel, {
// utility functions here
});

That’s it.

One last thing, please encourage the use of ‘var’ when creating variables.

I think you don’t need the ‘function MyGrid(config) {MyGrid.superclass.constructor.call(this,config)}’ line (in case you don’t override the constructor).

Just ‘MyGrid = Ext.extend(Ext.grid.GridPanel, MyTrait);’ should work in your example, too.

Never heard the name of Trait, in Ruby I would call this a module.

Cheers,
Steffen

Ext.reg(’my-grid’, MyGrid);

var myGrid = Ext.ComponentMgr.create({xtype: ‘my-grid’, title: “My Grid”});