JavaScript Error: Object expected

Question

I have an HTML page featuring a div with right-to-left scrolling text; the following JavaScript is located between the HEAD tags of the document.

function scroll(oid, iid) {
            this.oCont = document.getElementById(oid);
            this.ele = document.getElementById(iid);
            this.width = this.ele.clientWidth;
            this.n = this.oCont.clientWidth;
            this.move = function() {
                this.ele.style.left=this.n + "px"
                this.n--
                if(this.n<(-this.width)){this.n=this.oCont.clientWidth}
            }
        }
        var vScroll
        function setup() {
            vScroll = new scroll("oScroll", "scroll");
            setInterval("vScroll.move()", 20);
            }           
        onload = function(){
            setup()
        }

        $("scroll").hover(function() {
            $("scroll").stop(true, false)
        }, function(){
            scroll();
        });
        scroll();

The scrolling text works fine; however I wanted the scrolling to stop on mouse hover. Although the text does stop scrolling when the mouse cursor passes over the div, I get a javascript error "Object expected". I'm new to javascript and have no idea where I'm going wrong.

Any help would be greatly appreciated.

which line does the error point to? It looks like you're trying to reference this outside of the proper context — Sterling Archer
– Sterling Archer, Commented Sep 25, 2013 at 14:40
The page is actually being displayed in a WebBrowser control in a simple WPF application; I think this must be an IE browser; changing the default browser does not affect the functioning of the error message.. — The Furious Bear
– The Furious Bear, Commented Sep 25, 2013 at 14:45
@user1748443: Object expected is an IE error. All other browsers give a much more descriptive and useful error message. For example: Chrome says vScroll is not defined. — gen_Eric
– gen_Eric, Commented Sep 25, 2013 at 14:58

gen_Eric · Accepted Answer · 2013-09-25 14:45:55Z

1

Your problem is with your setInterval. You are passing it a string! This makes it use eval! That means the code is ran in global scope, so vScroll does not exist.

Instead, pass a function to setInterval:

setInterval(function(){
    vScroll.move();
}, 20);

The function passed to setInterval is called with the "context" (this value) set to null, so you cannot pass vScroll.move directly to setTimeout. You can, however. do:

setInterval(vScroll.move.bind(vScroll), 20);

but this doesn't work in all browsers.

P.S. Passing a string to setInterval is bad practice, you should always be passing a function.

answered Sep 25, 2013 at 14:45

gen_Eric

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