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HTML

              
                <p>The tiniest <a href="https://getbutterfly.com/how-to-build-a-vanilla-javascript-slider-in-less-than-100-lines/">Vanilla JavaScript Sliders</a>.</p>

<div class="wrap">
    <div class="swipe">
        <ul id="slider4">
            <li style="display:block"><img src="https://images.unsplash.com/photo-1533667586627-9f5ddbd42539?ixlib=rb-0.3.5&ixid=eyJhcHBfaWQiOjEyMDd9&s=bb707c0b87345277ebc415156111fb69&auto=format&fit=crop&w=1350&q=80" alt=""></li>
            <li><img src="https://images.unsplash.com/photo-1519643381401-22c77e60520e?ixlib=rb-0.3.5&ixid=eyJhcHBfaWQiOjEyMDd9&s=5a01717a33db39cbdabd468904b61d22&auto=format&fit=crop&w=1353&q=80" alt=""></li>
            <li><img src="https://images.unsplash.com/photo-1519302959554-a75be0afc82a?ixlib=rb-0.3.5&ixid=eyJhcHBfaWQiOjEyMDd9&s=249031677221bcb99a1fe56668c5c97b&auto=format&fit=crop&w=1362&q=80" alt=""></li>
            <li><img src="https://images.unsplash.com/photo-1517079495967-03aed29f98b5?ixlib=rb-0.3.5&ixid=eyJhcHBfaWQiOjEyMDd9&s=eb42f335f56f42f2abe66f4e6c2023b9&auto=format&fit=crop&w=1350&q=80" alt=""></li>
        </ul>
    </div>
    <br>
    <div id="pagenavi">
        <a href="#" class="active">1</a>
        <a href="#">2</a>
        <a href="#">3</a>
        <a href="#">4</a>
    </div>
    <br>
    <button class="btn btn-primary" onclick="t4.pause();">Pause</button>
    <button class="btn btn-primary" onclick="t4.play();">Play</button>
    <button class="btn btn-primary" onclick="t4.prev();">Previous</button>
    <button class="btn btn-primary" onclick="t4.next();">Next</button>
</div>

<script async type="text/javascript" src="//cdn.carbonads.com/carbon.js?serve=CESDK2J7&placement=getbutterflycom" id="_carbonads_js"></script>
              
            
!

CSS

              
                * {
    box-sizing: border-box;
}
body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif, "Segoe UI Symbol", "Apple Color Emoji", "Segoe UI Emoji";
    font-size: 14px;
    line-height: 1.5;
    color: #24292e;
    background-color: #fff;
}
input,
button {
    font-family: inherit;
    font-size: inherit;
}
.wrap {
    margin: 0 auto;
    padding: 0;
    width: 600px;
}

.swipe {
    margin: 0 auto;
    overflow: hidden;
    position: relative;
    width: 100%;
}
.swipe ul {
    overflow: hidden;
    margin: 0;
    padding: 0;
}
.swipe li div,
.swipe div div div {
    padding: 50px 10px;
    background: #1db1ff;
    font-weight: bold;
    color: #fff;
    font-size: 20px;
    text-align: center;
}
.swipe li img {
    width: 100%;
}
.swipe li {
    margin: 0;
    padding: 0;
}
#slider2 li {
    width: 230px;
}
#slider4 ul {
    transition: left 800ms ease-in 0;
}
#pagenavi a {
    display: inline-block;
    width: 80px;
    height: 60px;
    background-color: yellow;
}
#pagenavi a.active {
    color: red;
}

              
            
!

JS

              
                (function(ROOT, struct, undefined) {
    "use strict";

    var lastTime = 0,
        nextFrame =
            ROOT.requestAnimationFrame ||
            ROOT.webkitRequestAnimationFrame ||
            ROOT.mozRequestAnimationFrame ||
            ROOT.msRequestAnimationFrame ||
            function(callback) {
                var currTime = +new Date(),
                    delay = Math.max(
                        1000 / 60,
                        1000 / 60 - (currTime - lastTime)
                    );
                lastTime = currTime + delay;
                return setTimeout(callback, delay);
            },
        cancelFrame =
            ROOT.cancelAnimationFrame ||
            ROOT.webkitCancelAnimationFrame ||
            ROOT.webkitCancelRequestAnimationFrame ||
            ROOT.mozCancelRequestAnimationFrame ||
            ROOT.msCancelRequestAnimationFrame ||
            clearTimeout,
        DOC = ROOT.document,
        divstyle = DOC.createElement("div").style,
        cssVendor = (function() {
            var tests = "-webkit- -moz- -o- -ms-".split(" "),
                prop;
            while ((prop = tests.shift())) {
                if (camelCase(prop + "transform") in divstyle) {
                    return prop;
                }
            }
            return "";
        })(),
        transition = cssTest("transition"),
        toString = Object.prototype.toString,
        slice = [].slice,
        class2type = {},
        event2type = {},
        event2code = {
            click: 4,
            dommousescroll: 5,
            keydown: 6,
            resize: 7
        },
        POINTERTYPES = {
            2: "touch",
            3: "pen",
            4: "mouse",
            pen: "pen"
        },
        STARTEVENT = [],
        MOVEEVENT = [],
        EVENT = (function() {
            var ret = {},
                states = {
                    start: 1,
                    down: 1,
                    move: 2,
                    end: 3,
                    up: 3,
                    cancel: 3
                };
            each("mouse touch pointer MSPointer-".split(" "), function(prefix) {
                var _prefix = /pointer/i.test(prefix) ? "pointer" : prefix;
                ret[_prefix] = ret[_prefix] || {};
                POINTERTYPES[_prefix] = _prefix;
                each(states, function(endfix, code) {
                    var ev = camelCase(prefix + endfix);
                    ret[_prefix][ev] = code;
                    event2type[ev.toLowerCase()] = _prefix;
                    event2code[ev.toLowerCase()] = code;
                    if (code == 1) {
                        STARTEVENT.push(ev);
                    } else {
                        MOVEEVENT.push(ev);
                    }
                });
            });
            each(
                "otransitionend oTransitionEnd webkitTransitionEnd mozTransitionEnd MSTransitionEnd transitionend".split(
                    " "
                ),
                function(ev) {
                    STARTEVENT.push(ev);
                    event2code[ev.toLowerCase()] = 8;
                }
            );
            return ret;
        })(),
        POINTERS = {
            touch: {},
            pointer: {},
            mouse: {}
        };

    each(
        "Boolean Number String Function Array Date RegExp Object Error".split(
            " "
        ),
        function(name) {
            class2type["[object " + name + "]"] = name.toLowerCase();
        }
    );

    function type(obj) {
        if (obj == null) {
            return obj + "";
        }

        return typeof obj == "object" || typeof obj == "function"
            ? class2type[toString.call(obj)] || "object"
            : typeof obj;
    }

    function isArrayLike(elem) {
        var tp = type(elem);
        return (
            !!elem &&
            tp != "function" &&
            tp != "string" &&
            (elem.length === 0 ||
                (elem.length &&
                    (elem.nodeType == 1 || elem.length - 1 in elem)))
        );
    }

    function camelCase(str) {
        return (str + "")
            .replace(/^-ms-/, "ms-")
            .replace(/-([a-z]|[0-9])/gi, function(all, letter) {
                return (letter + "").toUpperCase();
            });
    }

    function cssTest(name) {
        var prop = camelCase(name),
            _prop = camelCase(cssVendor + prop);
        return (prop in divstyle && prop) || (_prop in divstyle && _prop) || "";
    }

    function isFunction(func) {
        return type(func) == "function";
    }

    function pointerLength(obj) {
        var len = 0,
            key;
        if (type(obj.length) == "number") {
            len = obj.length;
        } else if ("keys" in Object) {
            len = Object.keys(obj).length;
        } else {
            for (key in obj) {
                if (obj.hasOwnProperty(key)) {
                    len++;
                }
            }
        }
        return len;
    }

    function pointerItem(obj, n) {
        return "item" in obj
            ? obj.item(n)
            : function() {
                  var i = 0,
                      key;
                  for (key in this) {
                      if (i++ == n) {
                          return this[key];
                      }
                  }
              }.call(obj, n);
    }

    function each(arr, iterate) {
        if (isArrayLike(arr)) {
            if (type(arr.forEach) == "function") {
                return arr.forEach(iterate);
            }
            var i = 0,
                len = arr.length,
                item;
            for (; i < len; i++) {
                item = arr[i];
                if (type(item) != "undefined") {
                    iterate(item, i, arr);
                }
            }
        } else {
            var key;
            for (key in arr) {
                iterate(key, arr[key], arr);
            }
        }
    }

    function children(elem) {
        var ret = [];
        each(elem.children || elem.childNodes, function(elem) {
            if (elem.nodeType == 1) {
                ret.push(elem);
            }
        });
        return ret;
    }

    function getStyle(elem, prop) {
        var style =
            (ROOT.getComputedStyle && ROOT.getComputedStyle(elem, null)) ||
            elem.currentStyle ||
            elem.style;
        return style[prop];
    }

    function setStyle(elem, props) {
        each(props, function(name, value) {
            var prop;
            switch (name) {
                case "float":
                    prop = cssTest("cssFloat") ? "cssFloat" : "styleFloat";
                    break;
                default:
                    prop = camelCase(name);
            }
            try {
                elem.style[prop] = value;
            } catch (e) {}
        });
    }

    function addListener(elem, evstr, handler) {
        if (type(evstr) == "object") {
            return each(evstr, function(evstr, handler) {
                addListener(elem, evstr, handler);
            });
        }
        each(evstr.split(" "), function(ev) {
            if (elem.addEventListener) {
                elem.addEventListener(ev, handler, false);
            } else if (elem.attachEvent) {
                elem.attachEvent("on" + ev, handler);
            } else elem["on" + ev] = handler;
        });
    }

    function offListener(elem, evstr, handler) {
        if (type(evstr) == "object") {
            return each(evstr, function(evstr, handler) {
                offListener(elem, evstr, handler);
            });
        }
        each(evstr.split(" "), function(ev) {
            if (elem.removeEventListener) {
                elem.removeEventListener(ev, handler, false);
            } else if (elem.detachEvent) {
                elem.detachEvent("on" + ev, handler);
            } else elem["on" + ev] = null;
        });
    }

    function removeRange() {
        var range;
        if (ROOT.getSelection) {
            range = getSelection();
            if ("empty" in range) range.empty();
            else if ("removeAllRanges" in range) range.removeAllRanges();
        } else {
            DOC.selection.empty();
        }
    }

    function EASE(t, b, c, d) {
        return -c * ((t = t / d - 1) * t * t * t - 1) + b;
    }

    function filterEvent(oldEvent) {
        var ev = {},
            which = oldEvent.which,
            button = oldEvent.button,
            pointers,
            pointer;

        each("wheelDelta detail which keyCode".split(" "), function(prop) {
            ev[prop] = oldEvent[prop];
        });

        ev.oldEvent = oldEvent;

        ev.type = oldEvent.type.toLowerCase();
        ev.eventType = event2type[ev.type] || ev.type;
        ev.eventCode = event2code[ev.type] || 0;
        ev.pointerType =
            POINTERTYPES[oldEvent.pointerType] ||
            oldEvent.pointerType ||
            ev.eventType;

        ev.target =
            oldEvent.target || oldEvent.srcElement || DOC.documentElement;
        if (ev.target.nodeType === 3) {
            ev.target = ev.target.parentNode;
        }

        ev.preventDefault = function() {
            oldEvent.preventDefault && oldEvent.preventDefault();
            ev.returnValue = oldEvent.returnValue = false;
        };

        if ((pointers = POINTERS[ev.eventType])) {
            switch (ev.eventType) {
                case "mouse":
                case "pointer":
                    var id = oldEvent.pointerId || 0;
                    ev.eventCode == 3
                        ? delete pointers[id]
                        : (pointers[id] = oldEvent);
                    break;
                case "touch":
                    POINTERS[ev.eventType] = pointers = oldEvent.touches;
                    break;
            }

            if ((pointer = pointerItem(pointers, 0))) {
                ev.clientX = pointer.clientX;
                ev.clientY = pointer.clientY;
            }

            ev.button =
                which < 4
                    ? Math.max(0, which - 1)
                    : (button & 4 && 1) || button & 2; // left:0 middle:1 right:2
            ev.length = pointerLength(pointers);
        }

        return ev;
    }

    struct.prototype = {
        constructor: struct,
        latestTime: 0,
        init: function(config) {
            var self = this,
                handler = (this.handler = function(ev) {
                    self.handleEvent(ev);
                });

            this.events = {};
            this.duration = isNaN(parseInt(config.duration))
                ? 600
                : parseInt(config.duration);
            this.current = parseInt(config.start) || 0;
            this.mouse = config.mouse == null ? true : !!config.mouse;
            this.interval = parseInt(config.interval) || 5000;
            this.playing = config.autoplay == null ? true : !!config.autoplay;
            this.arrowkey = !!config.arrowkey;
            this.pages = children(this.container);
            this.length = this.pages.length;

            this.pageData = [];

            addListener(
                this.container,
                STARTEVENT.join(" ") + " click",
                handler
            );
            addListener(
                DOC,
                MOVEEVENT.join(" ") + (this.arrowkey ? " keydown" : ""),
                handler
            );
            addListener(ROOT, "resize", handler);

            each(this.pages, function(page) {
                self.pageData.push({
                    cssText: page.style.cssText || ""
                });
            });
            this.pageData.container = this.container.style.cssText || "";

            this.on({
                before: function() {
                    clearTimeout(this.playTimer);
                },
                dragStart: function() {
                    clearTimeout(this.playTimer);
                    removeRange();
                },
                after: this.firePlay
            }).firePlay();

            this.resize();
        },
        resize: function() {
            var self = this,
                pst = getStyle(this.container, "position"),
                css;

            this.size = this.getSize(
                (this.offsetParent =
                    this.container[
                        pst == "absolute" || pst == "fixed"
                            ? "offsetParent"
                            : "parentNode"
                    ] || DOC.body)
            );

            css = {
                float: "left",
                display: "inline"
            };
            each(this.pages, function(page) {
                css["width"] =
                    self.size -
                    self.getMarginSize(page) -
                    self.getPaddingSize(page) -
                    self.getBorderSize(page) +
                    "px";
                setStyle(page, css);
            });

            this.total = this.getSum(0, this.length);

            css = {};
            if (pst == "static") {
                css = { position: "relative" };
            }
            css[transition] = "none";
            css["width"] = this.total + "px";
            css["left"] = this.getPos(this.current) + "px";
            cancelFrame(this.timer);
            setStyle(this.container, css);

            clearTimeout(this.playTimer);

            return this.firePlay();
        },
        on: function(ev, callback) {
            var self = this;
            if (type(ev) == "object") {
                each(ev, function(ev, callback) {
                    self.on(ev, callback);
                });
            } else {
                if (!this.events[ev]) {
                    this.events[ev] = [];
                }
                this.events[ev].push(callback);
            }
            return this;
        },
        fire: function(ev) {
            var self = this,
                args = slice.call(arguments, 1);
            each(this.events[ev] || [], function(func) {
                if (isFunction(func)) {
                    func.apply(self, args);
                }
            });
            return this;
        },
        isStatic: function() {
            return !this.timer && !this.drag;
        },
        prev: function() {
            return this.slide((this.current - 1 + this.length) % this.length);
        },
        next: function() {
            return this.slide((this.current + 1) % this.length);
        },
        play: function() {
            this.playing = true;
            return this.firePlay();
        },
        firePlay: function() {
            var self = this;
            if (this.playing) {
                this.playTimer = setTimeout(function() {
                    self.next();
                }, this.interval);
            }
            return this;
        },
        pause: function() {
            this.playing = false;
            clearTimeout(this.playTimer);
            return this;
        },
        slide: function(_index) {
            var self = this,
                stime = +new Date(),
                duration = this.duration,
                current = this.current,
                index = Math.min(Math.max(0, _index), this.length - 1),
                curSize = this.getSum(index, index + 1),
                curPos = parseFloat(getStyle(this.container, "left")) || 0,
                css = {},
                tarPos;

            tarPos = this.getPos(index);
            duration *= Math.min(1, Math.abs(tarPos - curPos) / curSize) || 10;
            this.current = index;
            this.latestTime = stime + duration;
            this.fire("before", current, index);
            this.end = function() {
                delete self.timer;
                self.fire("after", index, current);
            };
            if (transition) {
                this.timer = 1;
                css[transition] = "left " + duration + "ms ease";
                css["left"] = tarPos + "px";
                setStyle(this.container, css);
            } else {
                cancelFrame(this.timer);
                ani();
            }

            function ani() {
                var offset = Math.min(duration, +new Date() - stime),
                    s = EASE(offset, 0, 1, duration);
                cp = (tarPos - curPos) * s + curPos;
                self.container.style["left"] = cp + "px";
                if (offset == duration) {
                    self.end();
                } else {
                    self.timer = nextFrame(ani);
                }
            }
        },
        handleEvent: function(oldEvent) {
            var ev = filterEvent(oldEvent),
                canDrag =
                    ev.button < 1 &&
                    ev.length < 2 &&
                    (!this.pointerType || this.pointerType == ev.eventType) &&
                    (this.mouse || ev.pointerType != "mouse");

            switch (ev.eventCode) {
                case 2:
                    if (canDrag && this.rect) {
                        var index = this.current,
                            rect = [ev.clientX, ev.clientY],
                            _rect = this.rect,
                            offset = rect[0] - _rect[0];
                        if (
                            this.drag == null &&
                            _rect.toString() != rect.toString()
                        ) {
                            this.drag =
                                Math.abs(offset) >=
                                Math.abs(rect[1] - _rect[1]);
                            this.drag && this.fire("dragStart", ev);
                        }
                        if (this.drag) {
                            if (!this.pages[index + (offset > 0 ? -1 : 1)]) {
                                offset /= Math.abs(offset) / this.size + 2;
                            }
                            this.container.style["left"] =
                                this.startPos + offset + "px";
                            this.fire("dragMove", ev);
                            this._offset = offset;
                            ev.preventDefault();
                        }
                    }
                    break;

                case 1:
                case 3:
                    if (canDrag) {
                        var self = this,
                            index = this.current,
                            isDrag,
                            offset,
                            tm,
                            nn,
                            sub,
                            curPos,
                            tarPos,
                            myWidth;
                        if (ev.length && (ev.eventCode == 1 || this.drag)) {
                            nn = ev.target.nodeName.toLowerCase();
                            clearTimeout(this.eventTimer);
                            if (!this.pointerType) {
                                this.pointerType = ev.eventType;
                            }
                            this.startPos =
                                parseFloat(getStyle(this.container, "left")) ||
                                0;
                            if (transition) {
                                this.container.style[transition] = "none";
                            } else if (this.timer) {
                                cancelFrame(this.timer);
                                delete this.timer;
                            }
                            this.rect = [ev.clientX, ev.clientY];
                            this.time = +new Date();
                            this.container.style["left"] = this.startPos + "px";
                            if (
                                ev.eventType != "touch" &&
                                (nn == "a" || nn == "img")
                            ) {
                                ev.preventDefault();
                            }
                        } else if ((tm = this.time)) {
                            offset = this._offset || 0;
                            isDrag = this.drag;
                            curPos = this.startPos + offset;
                            tarPos = this.getPos(index);

                            each(
                                "rect drag time startPos _offset".split(" "),
                                function(prop) {
                                    delete self[prop];
                                }
                            );

                            if (isDrag) {
                                sub = offset > 0 ? 1 : -1;
                                while (
                                    sub * (curPos - tarPos) >
                                        this.getOuterSize(this.pages[index]) /
                                            2 &&
                                    this.pages[index - sub]
                                ) {
                                    tarPos = this.getPos((index -= sub));
                                }

                                if (
                                    Math.abs(offset) > 20 &&
                                    +new Date() - tm < 500
                                ) {
                                    index -= sub;
                                }

                                this.fire("dragEnd", ev);
                                ev.preventDefault();
                            }

                            if (curPos != tarPos) {
                                this.slide(index);
                            } else if (isDrag) {
                                this.firePlay();
                            }

                            this.eventTimer = setTimeout(function() {
                                delete self.pointerType;
                            }, 400);
                        }
                    }
                    break;

                case 4:
                    if (this.timer) {
                        ev.preventDefault();
                    }
                    break;

                case 5:
                    ev.preventDefault();
                    if (
                        this.isStatic() &&
                        +new Date() - this.latestTime >
                            Math.max(1000 - this.duration, 0)
                    ) {
                        var wd = ev.wheelDelta || -ev.detail;
                        Math.abs(wd) >= 3 && this[wd > 0 ? "prev" : "next"]();
                    }
                    break;

                case 6:
                    var nn = ev.target.nodeName.toLowerCase();
                    if (
                        this.isStatic() &&
                        nn != "input" &&
                        nn != "textarea" &&
                        nn != "select"
                    ) {
                        switch (ev.keyCode || ev.which) {
                            case 33:
                            case 37:
                            case 38:
                                this.prev();
                                break;
                            case 32:
                            case 34:
                            case 39:
                            case 40:
                                this.next();
                                break;
                            case 35:
                                this.slide(this.length - 1);
                                break;
                            case 36:
                                this.slide(0);
                                break;
                        }
                    }
                    break;

                case 7:
                    this.resize();
                    break;

                case 8:
                    if (oldEvent.propertyName == "left") {
                        this.container.style[transition] = "none";
                        this.end();
                    }
                    break;
            }
        },
        getSum: function(from, to) {
            var sum = 0;
            while (from < to) {
                sum += this.getOuterSize(this.pages[from++], true);
            }
            return sum;
        },
        getPos: function(index) {
            var myWidth = this.getOuterSize(this.pages[index], true),
                sum =
                    this.getSum(0, index) +
                    this["getMarginLeftSize"](this.container) +
                    this["getBorderLeftSize"](this.container);

            return -sum;
        },
        getOuterSize: function(elem, withMargin) {
            return (
                elem["offsetWidth"] +
                (withMargin ? this.getMarginSize(elem) : 0)
            );
        },
        getInnerSize: function(elem) {
            return this.getOuterSize(elem) - this.getBorderSize(elem);
        },
        getSize: function(elem) {
            return (
                elem["offsetWidth"] -
                this.getPaddingSize(elem) -
                this.getBorderSize(elem)
            );
        },
        destroy: function() {
            var pageData = this.pageData;

            offListener(
                this.container,
                STARTEVENT.join(" ") + " click",
                this.handler
            );
            offListener(
                DOC,
                MOVEEVENT.join(" ") + (this.arrowkey ? " keydown" : ""),
                this.handler
            );
            offListener(ROOT, "resize", this.handler);

            each(this.pages, function(page, index) {
                page.style.cssText = pageData[index].cssText;
            });

            this.container.style.cssText = pageData.container;
            this.container.removeChild(this.comment);
            this.length = 0;

            return this.pause();
        },
        refresh: function() {
            this.pages = children(this.container);
            this.length = this.pages.length;
            this.current = Math.max(Math.min(this.length - 1, this.current), 0);
            return this.resize();
        },
        append: function(elem, index) {
            if (null == index) {
                index = this.pages.length;
            }
            this.pageData.splice(index, 0, {
                cssText: elem.style.cssText || ""
            });
            this.container.insertBefore(elem, this.pages[index] || null);

            return this.refresh();
        },
        prepend: function(elem) {
            return this.append(elem, 0);
        },
        insertBefore: function(elem, index) {
            return this.append(elem, index - 1);
        },
        insertAfter: function(elem, index) {
            return this.append(elem, index + 1);
        },
        remove: function(index) {
            this.container.removeChild(this.pages[index]);
            this.pageData.splice(index, 1);

            return this.refresh();
        }
    };

    each("margin padding border".split(" "), function(type) {
        each("Top Left Right Bottom".split(" "), function(dir) {
            var prop = type + dir;
            struct.prototype[camelCase("get-" + prop) + "Size"] = function(
                elem
            ) {
                return (
                    parseFloat(
                        getStyle(elem, prop + (type == "border" ? "Width" : ""))
                    ) || 0
                );
            };
        });
        struct.prototype[camelCase("get-" + type) + "Size"] = function(elem) {
            return (
                this[camelCase("get-" + type) + "Left" + "Size"](elem) +
                this[camelCase("get-" + type) + "Right" + "Size"](elem)
            );
        };
    });

    if (typeof define == "function" && define.amd) {
        define("TouchSlider", function() {
            return struct;
        });
    } else ROOT.TouchSlider = struct;
})(window, function(wrap, config) {
    if (!(this instanceof arguments.callee)) {
        return new arguments.callee(wrap, config);
    }

    this.container =
        typeof wrap == "string" ? document.getElementById(wrap) : wrap;
    this.init(config || {});
});

var thumbnails = document.querySelectorAll("#pagenavi a");

for (var i = 0; i < thumbnails.length; i++) {
    var parent = document.getElementById("slider4");
    var child = parent.querySelectorAll("li img");

    thumbnails[i].style.cssText =
        "background: url(" +
        child[i].src +
        ") no-repeat center center; background-size: cover;";
}

var active = 0,
    as = document.getElementById("pagenavi").getElementsByTagName("a");
for (var i = 0; i < as.length; i++) {
    (function() {
        var j = i;
        as[i].onclick = function() {
            t4.slide(j);
            return false;
        };
    })();
}

var t4 = new TouchSlider("slider4", { speed: 1000, interval: 6000 });
t4.on("before", function(m, n) {
    as[m].className = "";
    as[n].className = "active";
});

              
            
!
999px

Console