Arrays and Objects as Member Variables

If your class contains arrays or other objects, they should be declared in the constructor so that each instance gets it's own copy. Simple types (literal strings and numbers) and are fine to declare in the class directly.

/* GeSHi (C) 2004 - 2007 Nigel McNie (http://qbnz.com/highlighter) */ .geshifilter {font-family: monospace;} .geshifilter .imp {font-weight: bold; color: red;} .geshifilter .kw1 {color: #000066; font-weight: bold;} .geshifilter .kw2 {color: #003366; font-weight: bold;} .geshifilter .kw3 {color: #000066;} .geshifilter .co1 {color: #009900; font-style: italic;} .geshifilter .coMULTI {color: #009900; font-style: italic;} .geshifilter .es0 {color: #000099; font-weight: bold;} .geshifilter .br0 {color: #66cc66;} .geshifilter .st0 {color: #3366CC;} .geshifilter .nu0 {color: #CC0000;} .geshifilter .me1 {color: #006600;} .geshifilter .re0 {color: #0066FF;}

dojo.declare("my.classes.bar", my.classes.foo, {

        someData: [1, 2, 3, 4], // doesn't do what I want: ends up being static

        numItem : 5, // one per bar

        strItem : "string", // one per bar

         constructor: function() {

                this.someData = [ ]; // better, each bar has it's own array

                this.expensiveResource = new expensiveResource(); // one per bar 

        }

});

On the other hand, if you want an object or array to be static (shared between all instances of my.classes.bar), then you should do something like this:

dojo.declare("my.classes.bar", my.classes.foo, {

        constructor: function() {

                dojo.debug("this is bar object # " + this.statics.counter++);

        },

        statics: { counter: 0, somethingElse: "hello" }

});

"Statics" is not a special dojo construct - you can use any name you want, like "constants". In this example, you'd refer to the variable as myInstance.statics.counter both inside and outside the class definition.

Why is this true for arrays and objects, but not primitives? It's because, like most OOP languages, JavaScript uses object references. For example, given:

x = { fruit: "apple" };

y = x;

Now x and y both refer to the same object. Modifying x.fruit will also affect y.fruit.