Add a TruncatedList component, which truncates children passed to it.

src/components/views/elements/TruncatedList.js

@@ -0,0 +1,61 @@
+/*
+Copyright 2016 OpenMarket 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.
+*/
+var React = require('react');
+
+module.exports = React.createClass({
+    displayName: 'TruncatedList',
+
+    propTypes: {
+        truncateAt: React.PropTypes.number,
+        className: React.PropTypes.string,
+        createOverflowElement: React.PropTypes.func
+    },
+
+    getDefaultProps: function() {
+        return {
+            truncateAt: 2,
+            createOverflowElement: function(overflowCount, totalCount) {
+                return (
+                    <div>And {overflowCount} more...</div>
+                );
+            }
+        };
+    },
+
+    render: function() {
+        var childsJsx = this.props.children;
+        var overflowJsx;
+        var childCount = React.Children.count(this.props.children);
+        var overflowCount = childCount - this.props.truncateAt;
+
+        if (overflowCount > 0) {
+            overflowJsx = this.props.createOverflowElement(
+                overflowCount, childCount
+            );
+            var childArray = React.Children.toArray(this.props.children);
+            // cut out the overflow elements
+            childArray.splice(childCount - overflowCount, overflowCount);
+            childsJsx = childArray; // use what is left
+        }
+
+        return (
+            <div className={this.props.className}>
+                {childsJsx}
+                {overflowJsx}
+            </div>
+        );
+    }
+});