diff --git a/src/_h5ai/public/js/lib/ext/preview/preview-aud.js b/src/_h5ai/public/js/lib/ext/preview/preview-aud.js
index 446ae4c4..3bf6e6d9 100644
--- a/src/_h5ai/public/js/lib/ext/preview/preview-aud.js
+++ b/src/_h5ai/public/js/lib/ext/preview/preview-aud.js
@@ -10,22 +10,19 @@ const settings = Object.assign({
 }, allsettings['preview-aud']);
 const tpl = '<audio id="pv-content-aud"/>';
 
-let state;
-
 const updateGui = () => {
     const el = dom('#pv-content-aud')[0];
     if (!el) {
         return;
     }
 
-    preview.centerContent();
     preview.setLabels([
-        state.item.label,
+        preview.item.label,
         format.formatDate(el.duration * 1000, 'm:ss')
     ]);
 };
 
-const loadAudio = item => {
+const load = item => {
     return new Promise(resolve => {
         const $el = dom(tpl)
             .on('loadedmetadata', () => resolve($el))
@@ -38,16 +35,10 @@ const loadAudio = item => {
     });
 };
 
-const onEnter = (items, idx) => {
-    state = preview.state(items, idx, loadAudio, updateGui);
-};
-
 const init = () => {
-    if (!settings.enabled) {
-        return;
+    if (settings.enabled) {
+        preview.register(settings.types, load, updateGui);
     }
-
-    preview.register(settings.types, onEnter);
 };
 
 init();
diff --git a/src/_h5ai/public/js/lib/ext/preview/preview-img.js b/src/_h5ai/public/js/lib/ext/preview/preview-img.js
index 6202e604..1b4b5a5c 100644
--- a/src/_h5ai/public/js/lib/ext/preview/preview-img.js
+++ b/src/_h5ai/public/js/lib/ext/preview/preview-img.js
@@ -10,19 +10,15 @@ const settings = Object.assign({
 }, allsettings['preview-img']);
 const tpl = '<img id="pv-content-img"/>';
 
-let state;
-
 const updateGui = () => {
     const el = dom('#pv-content-img')[0];
     if (!el) {
         return;
     }
 
-    preview.centerContent();
-
     const elW = el.offsetWidth;
 
-    const labels = [state.item.label];
+    const labels = [preview.item.label];
     if (!settings.size) {
         const elNW = el.naturalWidth;
         const elNH = el.naturalHeight;
@@ -46,7 +42,7 @@ const requestSample = href => {
     });
 };
 
-const loadImage = item => {
+const load = item => {
     return Promise.resolve(item.absHref)
         .then(href => {
             return settings.size ? requestSample(href) : href;
@@ -58,16 +54,10 @@ const loadImage = item => {
         }));
 };
 
-const onEnter = (items, idx) => {
-    state = preview.state(items, idx, loadImage, updateGui);
-};
-
 const init = () => {
-    if (!settings.enabled) {
-        return;
+    if (settings.enabled) {
+        preview.register(settings.types, load, updateGui);
     }
-
-    preview.register(settings.types, onEnter);
 };
 
 init();
diff --git a/src/_h5ai/public/js/lib/ext/preview/preview-txt.js b/src/_h5ai/public/js/lib/ext/preview/preview-txt.js
index b238da1f..af7a3cf2 100644
--- a/src/_h5ai/public/js/lib/ext/preview/preview-txt.js
+++ b/src/_h5ai/public/js/lib/ext/preview/preview-txt.js
@@ -13,8 +13,6 @@ const settings = Object.assign({
 const tplPre = '<pre id="pv-content-txt"></pre>';
 const tplDiv = '<div id="pv-content-txt"></div>';
 
-let state;
-
 const updateGui = () => {
     const el = dom('#pv-content-txt')[0];
     if (!el) {
@@ -22,11 +20,11 @@ const updateGui = () => {
     }
 
     const container = dom('#pv-container')[0];
-    el.style.height = container.offsetHeight - 16 + 'px';
+    el.style.height = container.offsetHeight + 'px';
 
     preview.setLabels([
-        state.item.label,
-        state.item.size + ' bytes'
+        preview.item.label,
+        preview.item.size + ' bytes'
     ]);
 };
 
@@ -49,7 +47,7 @@ const requestTextContent = href => {
     });
 };
 
-const loadText = item => {
+const load = item => {
     return requestTextContent(item.absHref)
         .catch(err => '[request failed] ' + err)
         .then(content => {
@@ -71,16 +69,10 @@ const loadText = item => {
         });
 };
 
-const onEnter = (items, idx) => {
-    state = preview.state(items, idx, loadText, updateGui);
-};
-
 const init = () => {
-    if (!settings.enabled) {
-        return;
+    if (settings.enabled) {
+        preview.register(keys(settings.styles), load, updateGui);
     }
-
-    preview.register(keys(settings.styles), onEnter);
 };
 
 init();
diff --git a/src/_h5ai/public/js/lib/ext/preview/preview-vid.js b/src/_h5ai/public/js/lib/ext/preview/preview-vid.js
index dadea90f..3eb63ec2 100644
--- a/src/_h5ai/public/js/lib/ext/preview/preview-vid.js
+++ b/src/_h5ai/public/js/lib/ext/preview/preview-vid.js
@@ -9,28 +9,24 @@ const settings = Object.assign({
 }, allsettings['preview-vid']);
 const tpl = '<video id="pv-content-vid"/>';
 
-let state;
-
 const updateGui = () => {
     const el = dom('#pv-content-vid')[0];
     if (!el) {
         return;
     }
 
-    preview.centerContent();
-
     const elW = el.offsetWidth;
     const elVW = el.videoWidth;
     const elVH = el.videoHeight;
 
     preview.setLabels([
-        state.item.label,
+        preview.item.label,
         String(elVW) + 'x' + String(elVH),
         String((100 * elW / elVW).toFixed(0)) + '%'
     ]);
 };
 
-const loadVideo = item => {
+const load = item => {
     return new Promise(resolve => {
         const $el = dom(tpl)
             .on('loadedmetadata', () => resolve($el))
@@ -43,16 +39,10 @@ const loadVideo = item => {
     });
 };
 
-const onEnter = (items, idx) => {
-    state = preview.state(items, idx, loadVideo, updateGui);
-};
-
 const init = () => {
-    if (!settings.enabled) {
-        return;
+    if (settings.enabled) {
+        preview.register(settings.types, load, updateGui);
     }
-
-    preview.register(settings.types, onEnter);
 };
 
 init();
diff --git a/src/_h5ai/public/js/lib/ext/preview/preview.js b/src/_h5ai/public/js/lib/ext/preview/preview.js
index c1251c90..57cafb24 100644
--- a/src/_h5ai/public/js/lib/ext/preview/preview.js
+++ b/src/_h5ai/public/js/lib/ext/preview/preview.js
@@ -1,4 +1,4 @@
-const {each, isFn, isNum, dom, includes, compact} = require('../../util');
+const {each, isFn, dom, includes, compact} = require('../../util');
 const event = require('../../core/event');
 const resource = require('../../core/resource');
 const allsettings = require('../../core/settings');
@@ -26,14 +26,34 @@ const tplOverlay =
             </div>
         </div>`;
 const storekey = 'ext/preview';
+
 let isFullscreen = store.get(storekey) || false;
 let userAliveTimeoutId = null;
-let onIndexChange = null;
-let onAdjustSize = null;
-let spinnerVisible = false;
-let spinnerTimeoutId;
+let spinnerIsVisible = false;
+let spinnerTimeoutId = null;
+let session = null;
 
-const adjustSize = () => {
+const centerContent = () => {
+    const $container = dom('#pv-container');
+
+    const container = $container[0];
+    const content = $container.children()[0];
+    if (!container || !content) {
+        return;
+    }
+
+    const containerW = container.offsetWidth;
+    const containerH = container.offsetHeight;
+    const contentW = content.offsetWidth;
+    const contentH = content.offsetHeight;
+
+    dom(content).css({
+        left: (containerW - contentW) * 0.5 + 'px',
+        top: (containerH - contentH) * 0.5 + 'px'
+    });
+};
+
+const updateGui = () => {
     const docEl = win.document.documentElement;
     const winWidth = docEl.clientWidth;
     const winHeight = docEl.clientHeight;
@@ -60,11 +80,21 @@ const adjustSize = () => {
         dom('#pv-bar-fullscreen').find('img').attr('src', resource.image('preview-fullscreen'));
     }
 
-    if (isFn(onAdjustSize)) {
-        onAdjustSize();
+    centerContent();
+
+    if (isFn(session && session.adjust)) {
+        session.adjust();
     }
 };
 
+const setIndex = (idx, total) => {
+    dom('#pv-bar-idx').text(`${idx}/${total}`).show();
+};
+
+const setRawLink = href => {
+    dom('#pv-bar-raw').show().find('a').attr('href', href);
+};
+
 const setLabels = labels => {
     dom('#pv-buttons .bar-left').rm();
     each(labels, label => {
@@ -76,18 +106,6 @@ const setLabels = labels => {
     });
 };
 
-const onNext = () => {
-    if (isFn(onIndexChange)) {
-        onIndexChange(1);
-    }
-};
-
-const onPrevious = () => {
-    if (isFn(onIndexChange)) {
-        onIndexChange(-1);
-    }
-};
-
 const userAlive = () => {
     const $hof = dom('#pv-overlay .hof');
     win.clearTimeout(userAliveTimeoutId);
@@ -97,12 +115,15 @@ const userAlive = () => {
     }
 };
 
-const onFullscreen = () => {
+const next = () => session && session.moveIdx(1);
+const prev = () => session && session.moveIdx(-1);
+
+const toggleFullscreen = () => {
     isFullscreen = !isFullscreen;
     store.put(storekey, isFullscreen);
 
     userAlive();
-    adjustSize();
+    updateGui();
 };
 
 const dropEvent = ev => {
@@ -115,69 +136,45 @@ const onKeydown = ev => {
 
     if (key === 27) { // esc
         dropEvent(ev);
-        onExit(); // eslint-disable-line no-use-before-define
+        exit(); // eslint-disable-line no-use-before-define
     } else if (key === 8 || key === 37) { // backspace, left
         dropEvent(ev);
-        onPrevious();
+        prev();
     } else if (key === 13 || key === 32 || key === 39) { // enter, space, right
         dropEvent(ev);
-        onNext();
+        next();
     } else if (key === 70) { // f
         dropEvent(ev);
-        onFullscreen();
+        toggleFullscreen();
     }
 };
 
-const onEnter = () => {
+const enter = () => {
     setLabels([]);
     dom('#pv-container').clr();
     dom('#pv-overlay').show();
     dom(win).on('keydown', onKeydown);
-    adjustSize();
+    updateGui();
 };
 
-const onExit = () => {
+const exit = () => {
     setLabels([]);
     dom('#pv-container').clr();
     dom('#pv-overlay').hide();
     dom(win).off('keydown', onKeydown);
 };
 
-const setIndex = (idx, total) => {
-    if (isNum(idx)) {
-        dom('#pv-bar-idx').text(String(idx) + (isNum(total) ? '/' + String(total) : '')).show();
-    } else {
-        dom('#pv-bar-idx').text('').hide();
-    }
-};
-
-const setRawLink = href => {
-    if (href) {
-        dom('#pv-bar-raw').show().find('a').attr('href', href);
-    } else {
-        dom('#pv-bar-raw').hide().find('a').attr('href', '#');
-    }
-};
-
-const setOnIndexChange = fn => {
-    onIndexChange = fn;
-};
-
-const setOnAdjustSize = fn => {
-    onAdjustSize = fn;
-};
-
 const showSpinner = (show, src, delay) => {
     win.clearTimeout(spinnerTimeoutId);
     const $spinner = dom('#pv-spinner');
 
     if (!show) {
-        spinnerVisible = false;
+        spinnerIsVisible = false;
         $spinner.hide();
         return;
     }
 
-    if (!spinnerVisible && delay) {
+    if (!spinnerIsVisible && delay) {
         spinnerTimeoutId = win.setTimeout(() => showSpinner(true, src), delay);
         return;
     }
@@ -188,64 +185,25 @@ const showSpinner = (show, src, delay) => {
     } else {
         $back.hide();
     }
-    spinnerVisible = true;
+    spinnerIsVisible = true;
     $spinner.show();
 };
 
-const centerContent = () => {
-    const $container = dom('#pv-container');
-
-    const container = $container[0];
-    const content = $container.children()[0];
-    if (!container || !content) {
-        return;
-    }
-
-    const containerW = container.offsetWidth;
-    const containerH = container.offsetHeight;
-    const contentW = content.offsetWidth;
-    const contentH = content.offsetHeight;
-
-    dom(content).css({
-        left: (containerW - contentW) * 0.5 + 'px',
-        top: (containerH - contentH) * 0.5 + 'px'
-    });
-};
-
-const state = (items, idx, load, adjust) => {
-    const inst = Object.assign(Object.create(state.prototype), {items, load, adjust});
+const Session = (items, idx, load, adjust) => {
+    const inst = Object.assign(Object.create(Session.prototype), {items, load, adjust});
     inst.setIdx(idx);
-
-    setOnAdjustSize(adjust);
-    setOnIndexChange(delta => inst.moveIdx(delta));
-    onEnter();
-
-    return {
-        get item() {
-            return inst.item;
-        }
-    };
+    return inst;
 };
 
-state.prototype = {
+Session.prototype = {
     setIdx(idx) {
         this.idx = (idx + this.items.length) % this.items.length;
         this.item = this.items[this.idx];
-        this.updateGui();
-        this.updateContent();
-    },
 
-    moveIdx(delta) {
-        this.setIdx(this.idx + delta);
-    },
-
-    updateGui() {
-        setLabels([this.item.label]);
         setIndex(this.idx + 1, this.items.length);
         setRawLink(this.item.absHref);
-    },
+        setLabels([this.item.label]);
 
-    updateContent() {
         const item = this.item;
         Promise.resolve()
             .then(() => {
@@ -256,18 +214,20 @@ state.prototype = {
             // delay for testing
             // .then(x => new Promise(resolve => setTimeout(() => resolve(x), 1000)))
             .then($content => {
-                if (item !== this.item) {
-                    return;
+                if (item === this.item) {
+                    dom('#pv-container').clr().app($content).show();
+                    showSpinner(false);
+                    updateGui();
                 }
-                showSpinner(false);
-
-                dom('#pv-container').clr().app($content).show();
-                this.adjust();
             });
+    },
+
+    moveIdx(delta) {
+        this.setIdx(this.idx + delta);
     }
 };
 
-const register = (types, enter) => {
+const register = (types, load, adjust) => {
     const initItem = item => {
         if (item.$view && includes(types, item.type)) {
             item.$view.find('a').on('click', ev => {
@@ -278,7 +238,8 @@ const register = (types, enter) => {
                     return includes(types, matchedItem.type) ? matchedItem : null;
                 }));
 
-                enter(matchedItems, matchedItems.indexOf(item));
+                session = Session(matchedItems, matchedItems.indexOf(item), load, adjust);
+                enter();
             });
         }
     };
@@ -299,7 +260,7 @@ const init = () => {
         .on('mousedown', userAlive)
         .on('click', ev => {
             if (ev.target.id === 'pv-overlay' || ev.target.id === 'pv-container') {
-                onExit();
+                exit();
             }
         })
         .on('mousedown', dropEvent)
@@ -308,21 +269,22 @@ const init = () => {
         .on('keypress', dropEvent);
 
     dom('#pv-spinner').hide();
-    dom('#pv-bar-prev, #pv-prev-area').on('click', onPrevious);
-    dom('#pv-bar-next, #pv-next-area').on('click', onNext);
-    dom('#pv-bar-close').on('click', onExit);
-    dom('#pv-bar-fullscreen').on('click', onFullscreen);
+    dom('#pv-bar-prev, #pv-prev-area').on('click', prev);
+    dom('#pv-bar-next, #pv-next-area').on('click', next);
+    dom('#pv-bar-close').on('click', exit);
+    dom('#pv-bar-fullscreen').on('click', toggleFullscreen);
 
     dom(win)
-        .on('resize', adjustSize)
-        .on('load', adjustSize);
+        .on('resize', updateGui)
+        .on('load', updateGui);
 };
 
-init();
-
 module.exports = {
     setLabels,
-    centerContent,
-    state,
-    register
+    register,
+    get item() {
+        return session && session.item;
+    }
 };
+
+init();