Unable to make recursive call in Javascript

Question

When I try to run this program, I get an error in Firefox saying that:

moveDate is undefined on line 41

(referring to the line window.setTimeout("moveDate()",100);.

Any ideas why? I thought recursive functions were able to define themselves and then call upon themselves.

function monthScroller(){
    document.getElementById("month").style.visibility = "visible";
    var x = 0;
    var y = 0;
    var dest_x = window.innerWidth/2;
    var dest_y = window.innerHeight/2;  
    var interval = 1;

    function moveDate() {
        if(x<dest_x){ x = x + interval;} 
        if(y<dest_y){ y = y + interval;}

        document.getElementById("month").style.top  = y+"px";
        document.getElementById("month").style.left = x+"px";

        if ((x+interval < dest_x) && (y+interval < dest_y)) {
                window.setTimeout("moveDate()",100);
        }
        else{
            name();
        }
    }
    moveDate();
}

eval() is evil. Don't use those, including that one in setTimeout(""). — Derek 朕會功夫
– Derek 朕會功夫, Commented May 30, 2012 at 3:56
Derek, you beat me to the eval() is evil line. Anyway, this blog post explains more about why you don't want to use strings to evaluate code dynamically (which is what setTimeout does when you use a string). blogs.msdn.com/b/ericlippert/archive/2003/11/01/53329.aspx — Daniel Wolfe
– Daniel Wolfe, Commented May 30, 2012 at 3:57
It's not really recursive, moveDate() will complete its call about 100ms before it is run again from your setTimeout call if you follow the advice of the answerers. — Jason Goemaat
– Jason Goemaat, Commented May 30, 2012 at 3:58
@Derek—give it a rest. The "eval is evil" mantra started over a decade ago and was fundamentally not about evaluating strings in setTimeout and setInterval (and Function), they were side issues. The only problem with its use here relates to efficiency (ignoring the scope issue), none of the other "evilness" of eval is relevant here. — RobG
– RobG, Commented May 30, 2012 at 5:02

Derek 朕會功夫 · Accepted Answer · 2012-05-30 03:55:01Z

6

Yes, they are. Yet, window.setTimeout("moveDate()",100); will eval that code string in the global scope - no moveDate to be found there. Instead, pass the function reference to setTimout():

 window.setTimeout(moveDate, 100);

edited May 30, 2012 at 3:55

Derek 朕會功夫

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answered May 30, 2012 at 3:54

Bergi

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Comments

frosty · Accepted Answer · 2012-05-30 03:55:19Z

2

"moveDate" is scoped inside of the monthScroller method. Anything outside of the brackets of the monthScroller function can't see the "moveDate" function. So... when the setTimeout runs, the scope "window" and window doesn't have a function named "moveDate" in scope. What you need to do is change the call to the following:

setTimeout(moveDate,100);

That should work for you. That way you are passing the moveDate function/object into the setTimeout.

answered May 30, 2012 at 3:55

frosty

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