What is the point of declaring variables without assignment?

Question

I'm studying some CreateJS samples and in one of them I've seen this and I'm wondering what use it's for

(function() {
    var c = createjs;
    var a = function(blabla) {
        this.blabla = blabla;

    var p = Game.prototype;
    p.a;
    p.b;
    p.c;
    p.d;
    /*
    ... 15 variables like that ...
    */
    p.init = function(param) {
        /* blabla */
    }
    /*
    ...
    long code after that
    ...
    */
})();

It's on the github samples, in the /createjs/sandbox-master/PlanetaryGary directory, it's the file js/Game.js

Answer 1

I'm the original author of the code in question. This pattern comes down to the simple philosophy that good code is self-documenting.

It's worth a quick mention for those coming into this blind that those properties are not actually named a,b,c, etc. It's also worth mentioning that they are usually assigned a default value (though not in this particular case).

The up-front variable declarations explicitly define the fields that will be associated with the "class". This allows a developer to scan from the top down, and establish a mental model of the data the class operates on prior to looking at the methods that operate on it.

It provides a convenient, contextual place to hook doc comments, though the referenced code is not documented.

/**
 * Docs for firstName here.
 **/
p.firstName = "default";

/**
 * lastName docs.
 **/
p.lastName = "default";

Lastly, I've found it encourages a more thoughtful approach to data and documentation. The act of defining a new property becomes an opportunity to view the existing properties and evaluate the necessity of the new field. I've seen a lot of bugs and poor code result from devs appending properties to classes willy-nilly.

It's also a lot harder to forget to document new properties (and much easier to quickly spot undocumented properties) when you're explicitly defining them in a dedicated area of your code.