diff --git a/res/css/structures/_RoomSubList.scss b/res/css/structures/_RoomSubList.scss
index 2d471ee198..b7fe19ca89 100644
--- a/res/css/structures/_RoomSubList.scss
+++ b/res/css/structures/_RoomSubList.scss
@@ -33,13 +33,25 @@ limitations under the License.
 
 .mx_RoomSubList {
     min-height: 31px;
-    flex: 0 100000000 auto;
+    flex: 0 10000 auto;
     display: flex;
     flex-direction: column;
 }
 
+.mx_RoomSubList.resized-sized {
+    /*
+    flex-basis to 0 so sublists
+    are not shrinking/growing relative
+    to their content (as would be the case with auto),
+    as this intervenes with sizing an item exactly
+    when not available space is available
+    in the flex container
+    */
+    flex: 1 1 0;
+}
+
 .mx_RoomSubList_nonEmpty {
-    min-height: 70px;
+    min-height: 74px;
 
     .mx_AutoHideScrollbar_offset {
         padding-bottom: 4px;
@@ -50,17 +62,6 @@ limitations under the License.
     flex: none !important;
 }
 
-.mx_RoomSubList.resized-all {
-    flex: 0 1 auto;
-}
-
-.mx_RoomSubList.resized-sized {
-    /*  resizer set max-height on resized-sized,
-        so that limits the height and hence
-        needs a very small flex-shrink */
-    flex: 0 10000 auto;
-}
-
 .mx_RoomSubList_labelContainer {
     display: flex;
     flex-direction: row;
diff --git a/src/components/views/rooms/RoomList.js b/src/components/views/rooms/RoomList.js
index ed8142cd53..1a714e3a84 100644
--- a/src/components/views/rooms/RoomList.js
+++ b/src/components/views/rooms/RoomList.js
@@ -36,7 +36,7 @@ import GroupStore from '../../../stores/GroupStore';
 import RoomSubList from '../../structures/RoomSubList';
 import ResizeHandle from '../elements/ResizeHandle';
 
-import {Resizer, RoomDistributor, RoomSizer} from '../../../resizer'
+import {Resizer, RoomSubListDistributor} from '../../../resizer'
 const HIDE_CONFERENCE_CHANS = true;
 const STANDARD_TAGS_REGEX = /^(m\.(favourite|lowpriority|server_notice)|im\.vector\.fake\.(invite|recent|direct|archived))$/;
 
@@ -153,7 +153,11 @@ module.exports = React.createClass({
         if (typeof newSize === "string") {
             newSize = Number.MAX_SAFE_INTEGER;
         }
-        this.subListSizes[id] = newSize;
+        if (newSize === null) {
+            delete this.subListSizes[id];
+        } else {
+            this.subListSizes[id] = newSize;
+        }
         window.localStorage.setItem("mx_roomlist_sizes", JSON.stringify(this.subListSizes));
         // update overflow indicators
         this._checkSubListsOverflow();
@@ -164,7 +168,7 @@ module.exports = React.createClass({
         const cfg = {
             onResized: this._onSubListResize,
         };
-        this.resizer = new Resizer(this.resizeContainer, RoomDistributor, cfg, RoomSizer);
+        this.resizer = new Resizer(this.resizeContainer, RoomSubListDistributor, cfg);
         this.resizer.setClassNames({
             handle: "mx_ResizeHandle",
             vertical: "mx_ResizeHandle_vertical",
@@ -724,4 +728,4 @@ module.exports = React.createClass({
             </div>
         );
     },
-});
\ No newline at end of file
+});
diff --git a/src/resizer/distributors.js b/src/resizer/distributors.js
deleted file mode 100644
index caf677a18f..0000000000
--- a/src/resizer/distributors.js
+++ /dev/null
@@ -1,82 +0,0 @@
-/*
-Copyright 2018 New Vector Ltd
-
-Licensed under the Apache License, Version 2.0 (the "License");
-you may not use this file except in compliance with the License.
-You may obtain a copy of the License at
-
-    http://www.apache.org/licenses/LICENSE-2.0
-
-Unless required by applicable law or agreed to in writing, software
-distributed under the License is distributed on an "AS IS" BASIS,
-WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-See the License for the specific language governing permissions and
-limitations under the License.
-*/
-
-/**
-distributors translate a moving cursor into
-CSS/DOM changes by calling the sizer
-
-they have two methods:
-    `resize` receives then new item size
-    `resizeFromContainerOffset` receives resize handle location
-        within the container bounding box. For internal use.
-        This method usually ends up calling `resize` once the start offset is subtracted.
-the offset from the container edge of where
-the mouse cursor is.
-*/
-class FixedDistributor {
-    constructor(sizer, item, id, config) {
-        this.sizer = sizer;
-        this.item = item;
-        this.id = id;
-        this.beforeOffset = sizer.getItemOffset(this.item);
-        this.onResized = config && config.onResized;
-    }
-
-    resize(itemSize) {
-        this.sizer.setItemSize(this.item, itemSize);
-        if (this.onResized) {
-            this.onResized(itemSize, this.id, this.item);
-        }
-        return itemSize;
-    }
-
-    resizeFromContainerOffset(offset) {
-        this.resize(offset - this.beforeOffset);
-    }
-}
-
-
-class CollapseDistributor extends FixedDistributor {
-    constructor(sizer, item, id, config) {
-        super(sizer, item, id, config);
-        this.toggleSize = config && config.toggleSize;
-        this.onCollapsed = config && config.onCollapsed;
-        this.isCollapsed = false;
-    }
-
-    resize(newSize) {
-        const isCollapsedSize = newSize < this.toggleSize;
-        if (isCollapsedSize && !this.isCollapsed) {
-            this.isCollapsed = true;
-            if (this.onCollapsed) {
-                this.onCollapsed(true, this.item);
-            }
-        } else if (!isCollapsedSize && this.isCollapsed) {
-            if (this.onCollapsed) {
-                this.onCollapsed(false, this.item);
-            }
-            this.isCollapsed = false;
-        }
-        if (!isCollapsedSize) {
-            super.resize(newSize);
-        }
-    }
-}
-
-module.exports = {
-    FixedDistributor,
-    CollapseDistributor,
-};
diff --git a/src/resizer/distributors/collapse.js b/src/resizer/distributors/collapse.js
new file mode 100644
index 0000000000..784532a0eb
--- /dev/null
+++ b/src/resizer/distributors/collapse.js
@@ -0,0 +1,53 @@
+/*
+Copyright 2019 New Vector Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import FixedDistributor from "./fixed";
+import ResizeItem from "../item";
+
+class CollapseItem extends ResizeItem {
+    notifyCollapsed(collapsed) {
+        const callback = this.resizer.config.onCollapsed;
+        if (callback) {
+            callback(collapsed, this.id, this.domNode);
+        }
+    }
+}
+
+export default class CollapseDistributor extends FixedDistributor {
+    static createItem(resizeHandle, resizer, sizer) {
+        return new CollapseItem(resizeHandle, resizer, sizer);
+    }
+
+    constructor(item, config) {
+        super(item);
+        this.toggleSize = config && config.toggleSize;
+        this.isCollapsed = false;
+    }
+
+    resize(newSize) {
+        const isCollapsedSize = newSize < this.toggleSize;
+        if (isCollapsedSize && !this.isCollapsed) {
+            this.isCollapsed = true;
+            this.item.notifyCollapsed(true);
+        } else if (!isCollapsedSize && this.isCollapsed) {
+            this.item.notifyCollapsed(false);
+            this.isCollapsed = false;
+        }
+        if (!isCollapsedSize) {
+            super.resize(newSize);
+        }
+    }
+}
diff --git a/src/resizer/distributors/fixed.js b/src/resizer/distributors/fixed.js
new file mode 100644
index 0000000000..e93c6fbcee
--- /dev/null
+++ b/src/resizer/distributors/fixed.js
@@ -0,0 +1,55 @@
+/*
+Copyright 2019 New Vector Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import ResizeItem from "../item";
+import Sizer from "../sizer";
+
+/**
+distributors translate a moving cursor into
+CSS/DOM changes by calling the sizer
+
+they have two methods:
+    `resize` receives then new item size
+    `resizeFromContainerOffset` receives resize handle location
+        within the container bounding box. For internal use.
+        This method usually ends up calling `resize` once the start offset is subtracted.
+*/
+export default class FixedDistributor {
+    static createItem(resizeHandle, resizer, sizer) {
+        return new ResizeItem(resizeHandle, resizer, sizer);
+    }
+
+    static createSizer(containerElement, vertical, reverse) {
+        return new Sizer(containerElement, vertical, reverse);
+    }
+
+    constructor(item) {
+        this.item = item;
+        this.beforeOffset = item.offset();
+    }
+
+    resize(size) {
+        this.item.setSize(size);
+    }
+
+    resizeFromContainerOffset(offset) {
+        this.resize(offset - this.beforeOffset);
+    }
+
+    start() {}
+
+    finish() {}
+}
diff --git a/src/resizer/distributors/roomsublist.js b/src/resizer/distributors/roomsublist.js
new file mode 100644
index 0000000000..cc7875bfb0
--- /dev/null
+++ b/src/resizer/distributors/roomsublist.js
@@ -0,0 +1,132 @@
+/*
+Copyright 2019 New Vector Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import Sizer from "../sizer";
+import ResizeItem from "../item";
+
+class RoomSizer extends Sizer {
+    setItemSize(item, size) {
+        item.style.maxHeight = `${Math.round(size)}px`;
+        item.classList.add("resized-sized");
+    }
+
+    clearItemSize(item) {
+        item.style.maxHeight = null;
+        item.classList.remove("resized-sized");
+    }
+}
+
+class RoomSubListItem extends ResizeItem {
+    isCollapsed() {
+        return this.domNode.classList.contains("mx_RoomSubList_hidden");
+    }
+
+    maxSize() {
+        const header = this.domNode.querySelector(".mx_RoomSubList_labelContainer");
+        const scrollItem = this.domNode.querySelector(".mx_RoomSubList_scroll");
+        const headerHeight = this.sizer.getItemSize(header);
+        return headerHeight + (scrollItem ? scrollItem.scrollHeight : 0);
+    }
+
+    minSize() {
+        const isNotEmpty = this.domNode.classList.contains("mx_RoomSubList_nonEmpty");
+        return isNotEmpty ? 74 : 31; //size of header + 1? room tile (see room sub list css)
+    }
+
+    isSized() {
+        return this.domNode.classList.contains("resized-sized");
+    }
+}
+
+export default class RoomSubListDistributor {
+    static createItem(resizeHandle, resizer, sizer) {
+        return new RoomSubListItem(resizeHandle, resizer, sizer);
+    }
+
+    static createSizer(containerElement, vertical, reverse) {
+        return new RoomSizer(containerElement, vertical, reverse);
+    }
+
+    constructor(item) {
+        this.item = item;
+    }
+
+    _handleSize() {
+        return 1;
+    }
+
+    resize(size) {
+        //console.log("*** starting resize session with size", size);
+        let item = this.item;
+        while (item) {
+            const minSize = item.minSize();
+            if (item.isCollapsed()) {
+                item = item.previous();
+            } else if (size <= minSize) {
+                //console.log("  - resizing", item.id, "to min size", minSize);
+                item.setSize(minSize);
+                const remainder = minSize - size;
+                item = item.previous();
+                if (item) {
+                    size = item.size() - remainder - this._handleSize();
+                }
+            } else {
+                const maxSize = item.maxSize();
+                if (size > maxSize) {
+                    // console.log("  - resizing", item.id, "to maxSize", maxSize);
+                    item.setSize(maxSize);
+                    const remainder = size - maxSize;
+                    item = item.previous();
+                    if (item) {
+                        size = item.size() + remainder; // todo: handle size here?
+                    }
+                } else {
+                    //console.log("  - resizing", item.id, "to size", size);
+                    item.setSize(size);
+                    item = null;
+                    size = 0;
+                }
+            }
+        }
+        //console.log("*** ending resize session");
+    }
+
+    resizeFromContainerOffset(containerOffset) {
+        this.resize(containerOffset - this.item.offset());
+    }
+
+    start() {
+        // set all max-height props to the actual height.
+        let item = this.item.first();
+        const sizes = [];
+        while (item) {
+            if (!item.isCollapsed()) {
+                sizes.push(item.size());
+            } else {
+                sizes.push(100);
+            }
+            item = item.next();
+        }
+        item = this.item.first();
+        sizes.forEach((size) => {
+            item.setSize(size);
+            item = item.next();
+        });
+    }
+
+    finish() {
+    }
+}
diff --git a/src/resizer/index.js b/src/resizer/index.js
index 0720fa36ce..bc4c8f388c 100644
--- a/src/resizer/index.js
+++ b/src/resizer/index.js
@@ -14,17 +14,14 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {Sizer, FlexSizer} from "./sizer";
-import {FixedDistributor, CollapseDistributor} from "./distributors";
-import {Resizer} from "./resizer";
-import {RoomSizer, RoomDistributor} from "./room";
+import FixedDistributor from "./distributors/fixed";
+import CollapseDistributor from "./distributors/collapse";
+import RoomSubListDistributor from "./distributors/roomsublist";
+import Resizer from "./resizer";
 
 module.exports = {
     Resizer,
-    Sizer,
-    FlexSizer,
     FixedDistributor,
     CollapseDistributor,
-    RoomSizer,
-    RoomDistributor,
+    RoomSubListDistributor,
 };
diff --git a/src/resizer/item.js b/src/resizer/item.js
new file mode 100644
index 0000000000..2e06ad217c
--- /dev/null
+++ b/src/resizer/item.js
@@ -0,0 +1,107 @@
+/*
+Copyright 2019 New Vector Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+export default class ResizeItem {
+    constructor(handle, resizer, sizer) {
+        const id = handle.getAttribute("data-id");
+        const reverse = resizer.isReverseResizeHandle(handle);
+        const domNode = reverse ? handle.nextElementSibling : handle.previousElementSibling;
+
+        this.domNode = domNode;
+        this.id = id;
+        this.reverse = reverse;
+        this.resizer = resizer;
+        this.sizer = sizer;
+    }
+
+    _copyWith(handle, resizer, sizer) {
+        const Ctor = this.constructor;
+        return new Ctor(handle, resizer, sizer);
+    }
+
+    _advance(forwards) {
+        // opposite direction from fromResizeHandle to get back to handle
+        let handle = this.reverse ?
+            this.domNode.previousElementSibling :
+            this.domNode.nextElementSibling;
+        const moveNext = forwards !== this.reverse; // xor
+        // iterate at least once to avoid infinite loop
+        do {
+            if (moveNext) {
+                handle = handle.nextElementSibling;
+            } else {
+                handle = handle.previousElementSibling;
+            }
+        } while (handle && !this.resizer.isResizeHandle(handle));
+
+        if (handle) {
+            const nextHandle = this._copyWith(handle, this.resizer, this.sizer);
+            nextHandle.reverse = this.reverse;
+            return nextHandle;
+        }
+    }
+
+    next() {
+        return this._advance(true);
+    }
+
+    previous() {
+        return this._advance(false);
+    }
+
+    size() {
+        return this.sizer.getItemSize(this.domNode);
+    }
+
+    offset() {
+        return this.sizer.getItemOffset(this.domNode);
+    }
+
+    setSize(size) {
+        this.sizer.setItemSize(this.domNode, size);
+        const callback = this.resizer.config.onResized;
+        if (callback) {
+            callback(size, this.id, this.domNode);
+        }
+    }
+
+    clearSize() {
+        this.sizer.clearItemSize(this.domNode);
+        const callback = this.resizer.config.onResized;
+        if (callback) {
+            callback(null, this.id, this.domNode);
+        }
+    }
+
+
+    first() {
+        const firstHandle = Array.from(this.domNode.parentElement.children).find(el => {
+            return this.resizer.isResizeHandle(el);
+        });
+        if (firstHandle) {
+            return this._copyWith(firstHandle, this.resizer, this.sizer);
+        }
+    }
+
+    last() {
+        const lastHandle = Array.from(this.domNode.parentElement.children).reverse().find(el => {
+            return this.resizer.isResizeHandle(el);
+        });
+        if (lastHandle) {
+            return this._copyWith(lastHandle, this.resizer, this.sizer);
+        }
+    }
+}
diff --git a/src/resizer/resizer.js b/src/resizer/resizer.js
index 0e113b3664..4d999652a6 100644
--- a/src/resizer/resizer.js
+++ b/src/resizer/resizer.js
@@ -14,8 +14,6 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {Sizer} from "./sizer";
-
 /*
 classNames:
     // class on resize-handle
@@ -28,12 +26,14 @@ classNames:
     resizing: string
 */
 
-export class Resizer {
-    constructor(container, distributorCtor, distributorCfg, sizerCtor = Sizer) {
+
+export default class Resizer {
+    // TODO move vertical/horizontal to config option/container class
+    // as it doesn't make sense to mix them within one container/Resizer
+    constructor(container, distributorCtor, config) {
         this.container = container;
         this.distributorCtor = distributorCtor;
-        this.distributorCfg = distributorCfg;
-        this.sizerCtor = sizerCtor;
+        this.config = config;
         this.classNames = {
             handle: "resizer-handle",
             reverse: "resizer-reverse",
@@ -79,7 +79,11 @@ export class Resizer {
         }
     }
 
-    _isResizeHandle(el) {
+    isReverseResizeHandle(el) {
+        return el && el.classList.contains(this.classNames.reverse);
+    }
+
+    isResizeHandle(el) {
         return el && el.classList.contains(this.classNames.handle);
     }
 
@@ -99,6 +103,7 @@ export class Resizer {
         }
 
         const {sizer, distributor} = this._createSizerAndDistributor(resizeHandle);
+        distributor.start();
 
         const onMouseMove = (event) => {
             const offset = sizer.offsetFromEvent(event);
@@ -106,48 +111,33 @@ export class Resizer {
         };
 
         const body = document.body;
-        const onMouseUp = (event) => {
+        const finishResize = () => {
             if (this.classNames.resizing) {
                 this.container.classList.remove(this.classNames.resizing);
             }
-            body.removeEventListener("mouseup", onMouseUp, false);
+            distributor.finish();
+            body.removeEventListener("mouseup", finishResize, false);
+            document.removeEventListener("mouseleave", finishResize, false);
             body.removeEventListener("mousemove", onMouseMove, false);
         };
-        body.addEventListener("mouseup", onMouseUp, false);
+        body.addEventListener("mouseup", finishResize, false);
+        document.addEventListener("mouseleave", finishResize, false);
         body.addEventListener("mousemove", onMouseMove, false);
     }
 
     _createSizerAndDistributor(resizeHandle) {
         const vertical = resizeHandle.classList.contains(this.classNames.vertical);
-        const reverse = resizeHandle.classList.contains(this.classNames.reverse);
-
-        // eslint-disable-next-line new-cap
-        const sizer = new this.sizerCtor(this.container, vertical, reverse);
-
-        const items = this._getResizableItems();
-        const prevItem = resizeHandle.previousElementSibling;
-        // if reverse, resize the item after the handle instead of before, so + 1
-        const itemIndex = items.indexOf(prevItem) + (reverse ? 1 : 0);
-        const item = items[itemIndex];
-        const id = resizeHandle.getAttribute("data-id");
-        // eslint-disable-next-line new-cap
-        const distributor = new this.distributorCtor(
-            sizer, item, id, this.distributorCfg,
-            items, this.container);
+        const reverse = this.isReverseResizeHandle(resizeHandle);
+        const Distributor = this.distributorCtor;
+        const sizer = Distributor.createSizer(this.container, vertical, reverse);
+        const item = Distributor.createItem(resizeHandle, this, sizer);
+        const distributor = new Distributor(item, this.config);
         return {sizer, distributor};
     }
 
-    _getResizableItems() {
-        return Array.from(this.container.children).filter(el => {
-            return !this._isResizeHandle(el) && (
-                this._isResizeHandle(el.previousElementSibling) ||
-                this._isResizeHandle(el.nextElementSibling));
-        });
-    }
-
     _getResizeHandles() {
         return Array.from(this.container.children).filter(el => {
-            return this._isResizeHandle(el);
+            return this.isResizeHandle(el);
         });
     }
 }
diff --git a/src/resizer/room.js b/src/resizer/room.js
deleted file mode 100644
index def12d49eb..0000000000
--- a/src/resizer/room.js
+++ /dev/null
@@ -1,60 +0,0 @@
-/*
-Copyright 2018 New Vector Ltd
-
-Licensed under the Apache License, Version 2.0 (the "License");
-you may not use this file except in compliance with the License.
-You may obtain a copy of the License at
-
-    http://www.apache.org/licenses/LICENSE-2.0
-
-Unless required by applicable law or agreed to in writing, software
-distributed under the License is distributed on an "AS IS" BASIS,
-WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-See the License for the specific language governing permissions and
-limitations under the License.
-*/
-
-import {Sizer} from "./sizer";
-import {FixedDistributor} from "./distributors";
-
-class RoomSizer extends Sizer {
-    setItemSize(item, size) {
-        const isString = typeof size === "string";
-        const cl = item.classList;
-        if (isString) {
-            if (size === "resized-all") {
-                cl.add("resized-all");
-                cl.remove("resized-sized");
-                item.style.maxHeight = null;
-            }
-        } else {
-            cl.add("resized-sized");
-            cl.remove("resized-all");
-            item.style.maxHeight = `${Math.round(size)}px`;
-        }
-    }
-}
-
-class RoomDistributor extends FixedDistributor {
-    resize(itemSize) {
-        const scrollItem = this.item.querySelector(".mx_RoomSubList_scroll");
-        if (!scrollItem) {
-            return; //FIXME: happens when starting the page on a community url, taking the safe way out for now
-        }
-        const fixedHeight = this.item.offsetHeight - scrollItem.offsetHeight;
-        if (itemSize > (fixedHeight + scrollItem.scrollHeight)) {
-            super.resize("resized-all");
-        } else {
-            super.resize(itemSize);
-        }
-    }
-
-    resizeFromContainerOffset(offset) {
-        return this.resize(offset - this.sizer.getItemOffset(this.item));
-    }
-}
-
-module.exports = {
-    RoomSizer,
-    RoomDistributor,
-};
diff --git a/src/resizer/sizer.js b/src/resizer/sizer.js
index 303214854b..50861d34d5 100644
--- a/src/resizer/sizer.js
+++ b/src/resizer/sizer.js
@@ -18,31 +18,13 @@ limitations under the License.
 implements DOM/CSS operations for resizing.
 The sizer determines what CSS mechanism is used for sizing items, like flexbox, ...
 */
-class Sizer {
+export default class Sizer {
     constructor(container, vertical, reverse) {
         this.container = container;
         this.reverse = reverse;
         this.vertical = vertical;
     }
 
-    getItemPercentage(item) {
-        /*
-        const flexGrow = window.getComputedStyle(item).flexGrow;
-        if (flexGrow === "") {
-            return null;
-        }
-        return parseInt(flexGrow) / 1000;
-        */
-        const style = window.getComputedStyle(item);
-        const sizeStr = this.vertical ? style.height : style.width;
-        const size = parseInt(sizeStr, 10);
-        return size / this.getTotalSize();
-    }
-
-    setItemPercentage(item, percent) {
-        item.style.flexGrow = Math.round(percent * 1000);
-    }
-
     /**
         @param {Element} item the dom element being resized
         @return {number} how far the edge of the item is from the edge of the container
@@ -82,6 +64,14 @@ class Sizer {
         }
     }
 
+    clearItemSize(item) {
+        if (this.vertical) {
+            item.style.height = null;
+        } else {
+            item.style.width = null;
+        }
+    }
+
     /**
         @param {MouseEvent} event the mouse event
         @return {number} the distance between the cursor and the edge of the container,
@@ -96,12 +86,3 @@ class Sizer {
         }
     }
 }
-
-class FlexSizer extends Sizer {
-    setItemSize(item, size) {
-        item.style.flexGrow = `0`;
-        item.style.flexBasis = `${Math.round(size)}px`;
-    }
-}
-
-module.exports = {Sizer, FlexSizer};