How to prevent background scrolling when Bootstrap

Question

How to prevent background scrolling when Bootstrap 3 modal open on mobile platforms? On desktop browsers the background is prevented from scrolling and works as it should.

On mobile browsers (Safari ios, Chrome ios, etc), when a modal is opened and using your finger to scroll it, the background also scrolls as does the modal. How do I prevent that?

Answer 1

Courtesy of JDiApice who synthesized and extended the work of other contributors at iOS 8.x modal scroll issue #14839:

@media only screen and (max-device-width:768px) {

body.modal-open {
    // block scroll for mobile;
    // causes underlying page to jump to top;
    // prevents scrolling on all screens
    overflow: hidden;
    position: fixed;
    }
}

body.viewport-lg {
    // block scroll for desktop;
    // will not jump to top;
    // will not prevent scroll on mobile
    position: absolute;
}

body {
    overflow-x: hidden;
    overflow-y: scroll !important;
}

/* The reason the media specific is on there is 
   on a desktop i was having issues with when the modal would open 
   all content on the page would shift from centered to left. 
   Looked like crap. So this targets up to tablet size devices 
   where you would need to scroll. There is still a slight shift 
   on mobile and tablet but its really not much. */

Unlike the other solutions we tried, it does not scroll the background to the top after the popup modal closes.

Answer 2

I tried the accepted answer which prevented the body from scrolling but had the issue of scrolling to the top. This should solve both issues.

As a side note, it appears overflow:hidden doesn't work on body for iOS Safari only as iOS Chrome works fine.

var scrollPos = 0;

$('.modal')
    .on('show.bs.modal', function (){
        scrollPos = $('body').scrollTop();
        $('body').css({
            overflow: 'hidden',
            position: 'fixed',
            top : -scrollPos
        });
    })
    .on('hide.bs.modal', function (){
        $('body').css({
            overflow: '',
            position: '',
            top: ''
        }).scrollTop(scrollPos);
    });

Answer 3

If you use jQuery you can do this with scrollTop

1. Save the body's vertical scroll position;
2. Disable scroll on the body;
3. Show modal;
4. Close modal;
5. Reenable scroll on body;
6. Set saved scroll position.

#modal {
    bottom: 0;
    position: fixed;
    overflow-y: scroll;
    overflow-x: hidden;
    top: 0;
    width: 100%;
}

$('.open-modal').click(function (e) {
    e.preventDefault();
    $('#modal').toggle();
    scrollTo = $('body').scrollTop();
    $('body').css("position", "fixed");
});

$('.close-modal').click(function (e) {
    e.preventDefault();
    $('#modal').toggle();
    $('body').css("position", "static");
    $('body').animate({scrollTop: scrollTo}, 0);
});

Answer 4

Had an issue with this as well, iPhone + Safari where needed to add:

position: fixed;

As mentioned elsewhere, this created a scroll-to-top issue. Fix that worked for me was to capture the position to top upon modal open, and then animate to that position on modal close

upon modal open:

scrollTo = $('body').scrollTop();
$('body').css("position", "fixed");

upon modal close

$('body').css("position", "static");
$('body').animate({scrollTop: scrollTo}, 0);

Answer 5

The above answers did not help so what I did was:

.modal {
  -webkit-overflow-scrolling: touch; 
}

My particular problem was when I increased the modal size after loading.

It's a known iOS issue, see here. Since it does not break anything else the above solution was enough for my needs.

Answer 6

My solution...

Ver en jsfiddle

//Fix modal mobile Boostrap 3
function Show(id){
    //Fix CSS
    $(".modal-footer").css({"padding":"19px 20px 20px","margin-top":"15px","text-align":"right","border-top":"1px solid #e5e5e5"});
    $(".modal-body").css("overflow-y","auto");
    //Fix .modal-body height
    $('#'+id).on('shown.bs.modal',function(){
        $("#"+id+">.modal-dialog>.modal-content>.modal-body").css("height","auto");
        h1=$("#"+id+">.modal-dialog").height();
        h2=$(window).height();
        h3=$("#"+id+">.modal-dialog>.modal-content>.modal-body").height();
        h4=h2-(h1-h3);      
        if($(window).width()>=768){
            if(h1>h2){
                $("#"+id+">.modal-dialog>.modal-content>.modal-body").height(h4);
            }
            $("#"+id+">.modal-dialog").css("margin","30px auto");
            $("#"+id+">.modal-dialog>.modal-content").css("border","1px solid rgba(0,0,0,0.2)");
            $("#"+id+">.modal-dialog>.modal-content").css("border-radius",6);               
            if($("#"+id+">.modal-dialog").height()+30>h2){
                $("#"+id+">.modal-dialog").css("margin-top","0px");
                $("#"+id+">.modal-dialog").css("margin-bottom","0px");
            }
        }
        else{
            //Fix full-screen in mobiles
            $("#"+id+">.modal-dialog>.modal-content>.modal-body").height(h4);
            $("#"+id+">.modal-dialog").css("margin",0);
            $("#"+id+">.modal-dialog>.modal-content").css("border",0);
            $("#"+id+">.modal-dialog>.modal-content").css("border-radius",0);   
        }
        //Aply changes on screen resize (example: mobile orientation)
        window.onresize=function(){
            $("#"+id+">.modal-dialog>.modal-content>.modal-body").css("height","auto");
            h1=$("#"+id+">.modal-dialog").height();
            h2=$(window).height();
            h3=$("#"+id+">.modal-dialog>.modal-content>.modal-body").height();
            h4=h2-(h1-h3);
            if($(window).width()>=768){
                if(h1>h2){
                    $("#"+id+">.modal-dialog>.modal-content>.modal-body").height(h4);
                }
                $("#"+id+">.modal-dialog").css("margin","30px auto");
                $("#"+id+">.modal-dialog>.modal-content").css("border","1px solid rgba(0,0,0,0.2)");
                $("#"+id+">.modal-dialog>.modal-content").css("border-radius",6);               
                if($("#"+id+">.modal-dialog").height()+30>h2){
                    $("#"+id+">.modal-dialog").css("margin-top","0px");
                    $("#"+id+">.modal-dialog").css("margin-bottom","0px");
                }
            }
            else{
                //Fix full-screen in mobiles
                $("#"+id+">.modal-dialog>.modal-content>.modal-body").height(h4);
                $("#"+id+">.modal-dialog").css("margin",0);
                $("#"+id+">.modal-dialog>.modal-content").css("border",0);
                $("#"+id+">.modal-dialog>.modal-content").css("border-radius",0);   
            }
        };
    });  
    //Free event listener
    $('#'+id).on('hide.bs.modal',function(){
        window.onresize=function(){};
    });  
    //Mobile haven't scrollbar, so this is touch event scrollbar implementation
    var y1=0;
    var y2=0;
    var div=$("#"+id+">.modal-dialog>.modal-content>.modal-body")[0];
    div.addEventListener("touchstart",function(event){
        y1=event.touches[0].clientY;
    });
    div.addEventListener("touchmove",function(event){
        event.preventDefault();
        y2=event.touches[0].clientY;
        var limite=div.scrollHeight-div.clientHeight;
        var diff=div.scrollTop+y1-y2;
        if(diff<0)diff=0;
        if(diff>limite)diff=limite;
        div.scrollTop=diff;
        y1=y2;
    });
    //Fix position modal, scroll to top.    
    $('html, body').scrollTop(0);
    //Show
    $("#"+id).modal('show');
}