Run a method everytime value changes

Question

I wonder if any of you guys can help me with what I think is observing problem.

I have an element (svg to be more specific) that I want to update every time a value somewhere is changed.

I have variable: GetThreadTree().treeBoxObject.getFirstVisibleRow() that initially is 0. I want to run a function updateCanvas() every time value of GetThreadTree().treeBoxObject.getFirstVisibleRow() changes.

What I have is:

canvas.observe(GetThreadTree().treeBoxObject.getFirstVisibleRow(), "scroll", updateCanvas());

But it calls updateCanvas() only once, when it's called for the first time, and for some reason does not execute the code that is after it. I checked error console and nothing is there.

Any ideas?

Answer 1

One way of solving this problem is:

var registeredRow = 0;

function checkRow(){
    var row = GetThreadTree().treeBoxObject.getFirstVisibleRow();
    if (registeredRow != row) {
        registeredRow = row;
        updateCanvas();
    }
    window.setTimeout(checkRow, 1);
}

And before checkRow is called:

registeredRow = GetThreadTree().treeBoxObject.getFirstVisibleRow();
checkRow();

But it's not the most elegant solution but it works ;)