Question

I have a function where I am trying to create a scrolling effect on the div’s content by using an event for mouse wheel.

The listener:

document.getElementById('menu_base').addEventListener("mousewheel", scrollfunc, false);

I have this for my scroll event:

function scrollfunc(e){
console.log(e);
        if(e.wheelDeltaY == 120) { //this does work
            document.getElementById('menu_base').style.marginTop += 50; //no change
        } else if(e.wheelDeltaY == -120){ //as does this
            document.getElementById('menu_base').style.marginTop -= 50; //no change
        }           
}

The console.log shows:

WheelEvent {webkitDirectionInvertedFromDevice: false, wheelDeltaY: -120, wheelDeltaX: 0, wheelDelta: -120, webkitMovementY: 0…}

menu_base properties are:

.menu_base{
    width:100%;
    height:600px;   
    position:absolute; 
    left: 0; 
    top: 0;     
    text-align:center;
    border:1px solid black;
    overflow:hidden;
}

Yet the content does not move, marginTop does not seem to alter.

Any suggestions on what might be the probable cause ?

Answer 1

You need to define the marginTop with an unit, e.g. using px:

var menu_base = document.getElementById('menu_base');

function scrollfunc(e) {
    console.log(e);
    var mtop = parseInt(menu_base.style.marginTop, 10) || 0;

    if (e.wheelDeltaY == 120) { //this does work
        mtop += 50; //no change
    } else if (e.wheelDeltaY == -120) { //as does this
        mtop -= 50; //no change
    }
    menu_base.style.marginTop = mtop + 'px';
}

Fiddle