Detect left/right-swipe on touch-devices, but allow up/down-scrolling

Question

I need to detect and react to left/right-swipes, but want to give the user the ability to scroll on the same element, so as long as he moves his finger only left/right with a maximum up/down movement of X pixels, it should not scroll, but when he exceeds X, it should scroll.

So what I did is:

var startX, startY, $this = $(this);
function touchmove(event) {
        var touches = event.originalEvent.touches;
        if (touches && touches.length) {
            var deltaX = touches[0].pageX - startX;
            var deltaY = touches[0].pageY - startY;
            if (Math.abs(deltaY) > 50) {
                $this.html('X: ' + deltaX + '<br> Y: ' + deltaY + '<br>TRUE');
                $this.unbind('touchmove', touchmove);
                return true;
            } else {
                $this.html('X: ' + deltaX + '<br> Y: ' + deltaY);
                event.preventDefault();
            }
        }
    }

    function touchstart(event) {
        var touches = event.originalEvent.touches;
        if (touches && touches.length) {
            startX = touches[0].pageX;
            startY = touches[0].pageY;
            $this.bind('touchmove', touchmove);
        }
        //event.preventDefault();
    }

But I doesn't restore the ability to scroll in the "if" case...

Thanks for any tips.

Answer 1

I wrote my own touch handler events.maybe this helps you

it checks for:

fast click : 'fc'

swipe left : 'swl'

swipe right : 'swr'

swipe up : 'swu'

swipe down : 'swd'

each check initializes it's correspondent event.but you can scroll and do whatever else you do normally. you just have some new events.

you need swl swr, I aslo suggest to use fc (fastclick) for click events... it's much faster than normal click.

window.onload = function() {
    (function(d) {
        var
            ce = function(e, n) {
                var a = document.createEvent("CustomEvent");
                a.initCustomEvent(n, true, true, e.target);
                e.target.dispatchEvent(a);
                a = null;
                return false
            },
            nm = true,
            sp = {
                x: 0,
                y: 0
            },
            ep = {
                x: 0,
                y: 0
            },
            touch = {
                touchstart: function(e) {
                    sp = {
                        x: e.touches[0].pageX,
                        y: e.touches[0].pageY
                    }
                },
                touchmove: function(e) {
                    nm = false;
                    ep = {
                        x: e.touches[0].pageX,
                        y: e.touches[0].pageY
                    }
                },
                touchend: function(e) {
                    if (nm) {
                        ce(e, 'fc')
                    } else {
                        var x = ep.x - sp.x,
                            xr = Math.abs(x),
                            y = ep.y - sp.y,
                            yr = Math.abs(y);
                        if (Math.max(xr, yr) > 20) {
                            ce(e, (xr > yr ? (x < 0 ? 'swl' : 'swr') : (y < 0 ? 'swu' : 'swd')))
                        }
                    };
                    nm = true
                },
                touchcancel: function(e) {
                    nm = false
                }
            };
        for (var a in touch) {
            d.addEventListener(a, touch[a], false);
        }
    })(document);
    //EXAMPLE OF USE
    var h = function(e) {
        console.log(e.type, e)
    };
    document.body.addEventListener('fc', h, false); // 0-50ms vs 500ms with normal click
    document.body.addEventListener('swl', h, false);
    document.body.addEventListener('swr', h, false);
    document.body.addEventListener('swu', h, false);
    document.body.addEventListener('swd', h, false);
}

in this case h is my handler for every type of event and i add the handlers to the body.

for what i understand your question you just have to write

YOURELEMENT.addEventListener('swr',YOURSWIPERIGHTFUNCTION,false);
YOURELEMENT.addEventListener('swl',YOURSWIPELEFTFUNCTION,false);

to handle multiple elements and the same function... just add one handler.

so if you have

<ul id="ul"><li>1</li><li>2</li><li>3</li></ul>

you do:

var deleteli=function(e){
    var li=e.target;
    console.log('deleting '+li.textContent);
}
document.getElementById('ul').addEventListener('swl',deleteli,false);

same for fc & swr

there is a bug in ios: don't use alert() .. it will execute 2 times.

Answer 2

There is a "bug" in the accepted answer. If you don't use Chrome on Android but the build in browser or a "webview" (For a html5-hybrid-app) for example, then the swipe is not being detected.

I found out that the event doesn't fire, because of the normal scroll behavior. So adding "e.preventDefault();" in touchmove would fix it or the fix from Eric Fuller in the accepted answer.

It's a nice snipped but in a mobile WebApp or Website this could result in a bad scroll stuttering, because the touch-events are observed the whole time.

So I decided to build something new. It's not as comfortable like to have new event listeners, but it's comfortable enough for my needs and it's performat.

function detectswipe(el,func) {
  swipe_det = new Object();
  swipe_det.sX = 0;
  swipe_det.sY = 0;
  swipe_det.eX = 0;
  swipe_det.eY = 0;
  var min_x = 20;  //min x swipe for horizontal swipe
  var max_x = 40;  //max x difference for vertical swipe
  var min_y = 40;  //min y swipe for vertical swipe
  var max_y = 50;  //max y difference for horizontal swipe
  var direc = "";
  ele = document.getElementById(el);
  ele.addEventListener('touchstart',function(e){
    var t = e.touches[0];
    swipe_det.sX = t.screenX; 
    swipe_det.sY = t.screenY;
  },false);
  ele.addEventListener('touchmove',function(e){
    e.preventDefault();
    var t = e.touches[0];
    swipe_det.eX = t.screenX; 
    swipe_det.eY = t.screenY;    
  },false);
  ele.addEventListener('touchend',function(e){
    //horizontal detection
    if ((((swipe_det.eX - min_x > swipe_det.sX) || (swipe_det.eX + min_x < swipe_det.sX)) && ((swipe_det.eY < swipe_det.sY + max_y) && (swipe_det.sY > swipe_det.eY - max_y)))) {
      if(swipe_det.eX > swipe_det.sX) direc = "r";
      else direc = "l";
    }
    //vertical detection
    if ((((swipe_det.eY - min_y > swipe_det.sY) || (swipe_det.eY + min_y < swipe_det.sY)) && ((swipe_det.eX < swipe_det.sX + max_x) && (swipe_det.sX > swipe_det.eX - max_x)))) {
      if(swipe_det.eY > swipe_det.sY) direc = "d";
      else direc = "u";
    }

    if (direc != "") {
      if(typeof func == 'function') func(el,direc);
    }
    direc = "";
  },false);  
}

myfunction(el,d) {
  alert("you swiped on element with id '"+el+"' to "+d+" direction");
}

To use the function just use it like

detectswipe('an_element_id',myfunction);

detectswipe('an_other_element_id',my_other_function);

If a swipe is detected the function "myfunction" is called with parameter element-id and "l,r,u,d" (left,right,up,down).

Example: http://jsfiddle.net/rvuayqeo/1/