Question

Is there a way to have a static variable in a dojo (1.8) module so that I can retain state?

Example, say I set some value in some/module

require([
     'some/module'
], function (module) {
    module.setSomeValue(3); 
});

.. and then want to retrieve it later

define([
    'some/module'
], function(module) {
    return {
        start: function() {
            var x = module.getSomeValue(); 
        }
    };
});

A solution that works but seems like a hack,

acompany = window.acompany || {};
acompany.project = acompany.project || {
};

require([       
], function() {
    var debug = false;

    acompany.project.module = {
        /* static variables and functions here */ 
    };
});

define([

], function () {
    return acompany.project.module;
});

Answer 1

Actually there is always only single instance of AMD module, because (source):

define has two additional important characteristics that may not be immediately obvious:

• Module creation is lazy and asynchronous, and does not occur immediately when define is called. This means that factory is not executed, and any dependencies of the module will not be resolved, until some running code actually requires the module.
• Once a module value has been entered into the module namespace, it is not recomputed each time it is demanded. On a practical level, this means that factory is only invoked once, and the returned value is cached and shared among all code that uses a given module. (Note: the dojo loader includes the nonstandard function require.undef, which undefines a module value.)

In addition you do not have to provide just factory function, you can provide an object literal as well:

define("some/module", {
    someValue: "some",
    otherValue: "other"
});

Then somewhere else in your code:

require(["some/module"], function(module) {
    console.log("module.someValue", module.someValue); // some
    module.someValue = "some changed";
});

require(["some/module"], function(module) {
    console.log("module.someValue", module.someValue); // some changed
});

More robust solution includes an instance of dojo/Stateful, so you can watch for changes and define custom setters and getters:

define("some/stateful-module", ["dojo/Stateful"], function(Stateful){
    var stateful = new Stateful({
        someValue: "some",
        otherValue: "other"       
    });
    return stateful;
});

Then somewhere else in your code:

require(["some/stateful-module"], function(module) {
    console.log("stateful-module.someValue:", module.get("someValue"));
    module.watch(function(name, oldValue, newValue) {
        console.log("stateful-module: property"
            , name
            , "changed from"
            , "'" + oldValue + "'"
            ,  "to"
            , "'" + newValue + "'"
        );        
    });
});

require(["some/stateful-module"], function(module) {
    module.set("someValue", "some changed");
});​

See how it works at jsFiddle: http://jsfiddle.net/phusick/fHvZf/. It’s in a single file there, but it will work the same way across the whole application unless you require.undef(mid) the module.