Question

I’ve been looking through some library javascript source code and I’ve found a statement that I totally don’t understand. This library is based on dojo and uses its implementation of “class inheritance”. Here is a simplified version of code that is a subject:

dojo.declare("myCustomClass", {
    constructor:function(){
        // what does this statement mean?
        isContentShowing : false;

        //here some code that uses isContentShowing in callbacks
        dojo.connect(this, "fakeEvent", this, function(){
            if(this.isContentShowing){
            //do some stuff
            }
            //do more stuff
        });
    }
});

So the question is what does the isContentShowing: false; inside function body mean?

Answer 1

It’s not a variable. It is a label:

Provides a statement with an identifier that you can refer to using a break or continue statement.

In this case, it is useless: it is not used as a label, it does not perform an assignment, and the result of evaluating false is discarded.

I suspect a = and this are desired as this.isContentShowing = false makes more sense given the conditional below. Perhaps the original author never ran into/realized this bug due to this.isContentShowing evaluating to undefined (and thus still being falsey, like, well, false) later on.

Or, as Chris suggests in a comment, the intent might have been:

dojo.declare("myCustomClass", {
  isContentShowing : false, // but , and not ;
  constructor:...
});