---
title: "Javascript Timeline Event Grouping & Bulk Actions Example | Mobiscroll"
component: "Timeline"
framework: "JavaScript"
library_version: "6.1.5"
url: "https://demo.mobiscroll.com/javascript/timeline/event-grouping-bulk-action"
---

# Event Grouping & Bulk Actions - JavaScript Timeline demo

Group Javascript Timeline events into collapsible client/quarter blocks and bulk-drag groups — switch between assignee and work-type views on a full-year layout. Plain JS api for usage everywhere.

- [Live demo](https://demo.mobiscroll.com/javascript/timeline/event-grouping-bulk-action)
- [View code on GitHub](https://github.com/acidb/mobiscroll-demos-javascript/tree/main/src/demos/eventcalendar/timeline/event-grouping-bulk-action)
- This demo in other frameworks: [jQuery](https://demo.mobiscroll.com/jquery/timeline/event-grouping-bulk-action.md), [Angular](https://demo.mobiscroll.com/angular/timeline/event-grouping-bulk-action.md), [React](https://demo.mobiscroll.com/react/timeline/event-grouping-bulk-action.md), [Vue](https://demo.mobiscroll.com/vue/timeline/event-grouping-bulk-action.md)

## Description

When managing a large volume of events across multiple clients and time periods, handling items one by one quickly becomes inefficient. Users often need to move entire sets of related tasks together, not individual events. To support this, grouping and bulk interaction are essential.

The starting point is being able to look at the same dataset through different lenses. The demo supports switching between an assignee view, where each row represents a person responsible for the work, and a work type view, where each row represents a task category. A segmented control in the header allows adjusting the time granularity of the timeline while keeping a full year in view, enabling users to switch between quarterly, monthly, or weekly breakdowns. The view selector, grouping toggle, and segmented control are all rendered via the [`renderHeader`](https://mobiscroll.com/docs/javascript/eventcalendar/timeline#renderer-renderHeader) function, keeping the controls integrated into the timeline header. The [`renderResource` function](https://mobiscroll.com/docs/javascript/eventcalendar/timeline#renderer-renderResource) adapts the resource column accordingly, displaying employee avatars and job titles in assignee view, and work type color indicators in type view.

Once the right perspective is selected, individual events are not rendered one by one. Using the [`renderTimelineEvent`](https://mobiscroll.com/docs/javascript/eventcalendar/timeline#renderer-renderTimelineEvent) function, related tasks are automatically grouped into consolidated blocks per client and per quarter. These blocks can be expanded to reveal the individual tasks inside, or collapsed to keep the timeline readable at scale.

With grouping in place, bulk interaction becomes natural. An entire grouped block can be dragged along the timeline, moving all underlying events simultaneously. The system calculates the time delta and applies it uniformly to every event in the group. At the same time, individual tasks within a group remain accessible and can be edited through the edit button, which opens a range picker to update the event dates. Because both views are projections of the same event store, a change made in one view is immediately reflected in the other.

## What this demo shows

- A desktop monthly timeline for event grouping and bulk actions, with January to December months arranged horizontally and resources arranged vertically on the left.
- **Header navigation** The year label in the top left opens month navigation, while the blue previous and next arrows and the Today button on the right make it easy to move between months and jump back to the current day.
- **Custom parts of the header** In the header there are three custom options all arranged to the right but before the navigation arrows and today button: a checkable Group by Client/Quarter option, allows related projects to be organized by customer and reporting period. Next to it a dropdown select from which the user can select to show resourses view by ASssignee or View by Type. The last option is a segmented button with which you can change the zoom level of the calendar by default is set to Monthly, but you can change to Quearterly or Weekly.
- **Month view** The fixed strip below the header shows the selected years months from January to December, with the current month highlighted.

## Best for

- **Portfolio management** Reviewing client or portfolio-level work across a full year while keeping individual projects available on demand.
- **Program planning** Coordinating multiple related projects by customer, quarter, assignee, or project type.
- **Enterprise project roadmaps** Showing long-running initiatives with expandable summary rows and detailed project cards in the same timeline.
- **Capital project tracking** Planning installation, maintenance, inspection, upgrade, and repair work across months or quarters.
- **Long-term resource planning** Comparing workload by employee or work category without changing the underlying project data.
- **Bulk schedule adjustments** Moving grouped project work together when related tasks need to shift as a set.

## API used in this demo

- [`theme`](https://mobiscroll.com/docs/javascript/eventcalendar/api#opt-theme) - option
- [`themeVariant`](https://mobiscroll.com/docs/javascript/eventcalendar/api#opt-themeVariant) - option
- [`setOptions`](https://mobiscroll.com/docs/javascript/eventcalendar/api#method-setOptions) - method
- [`data`](https://mobiscroll.com/docs/javascript/eventcalendar/api#opt-data) - option
- [`resources`](https://mobiscroll.com/docs/javascript/eventcalendar/api#opt-resources) - option
- [`renderTimelineEvent`](https://mobiscroll.com/docs/javascript/eventcalendar/api#renderer-renderTimelineEvent) - renderer
- [`view`](https://mobiscroll.com/docs/javascript/eventcalendar/api#opt-view) - option
- [`dragBetweenResources`](https://mobiscroll.com/docs/javascript/eventcalendar/api#opt-dragBetweenResources) - option
- [`dragToMove`](https://mobiscroll.com/docs/javascript/eventcalendar/api#opt-dragToMove) - option
- [`dragToResize`](https://mobiscroll.com/docs/javascript/eventcalendar/api#opt-dragToResize) - option
- [`dragToCreate`](https://mobiscroll.com/docs/javascript/eventcalendar/api#opt-dragToCreate) - option
- [`clickToCreate`](https://mobiscroll.com/docs/javascript/eventcalendar/api#opt-clickToCreate) - option
- [`renderResource`](https://mobiscroll.com/docs/javascript/eventcalendar/api#renderer-renderResource) - renderer
- [`renderHeader`](https://mobiscroll.com/docs/javascript/eventcalendar/api#renderer-renderHeader) - renderer
- [`onEventUpdate`](https://mobiscroll.com/docs/javascript/eventcalendar/api#event-onEventUpdate) - event
- [`setEvents`](https://mobiscroll.com/docs/javascript/eventcalendar/api#method-setEvents) - method
- [`controls`](https://mobiscroll.com/docs/javascript/datepicker/api#opt-controls) - option
- [`select`](https://mobiscroll.com/docs/javascript/datepicker/api#opt-select) - option
- [`display`](https://mobiscroll.com/docs/javascript/datepicker/api#opt-display) - option
- [`touchUi`](https://mobiscroll.com/docs/javascript/datepicker/api#opt-touchUi) - option
- [`showRangeLabels`](https://mobiscroll.com/docs/javascript/datepicker/api#opt-showRangeLabels) - option
- [`onChange`](https://mobiscroll.com/docs/javascript/datepicker/api#event-onChange) - event
- [`setOptions`](https://mobiscroll.com/docs/javascript/datepicker/api#method-setOptions) - method
- [`headerText`](https://mobiscroll.com/docs/javascript/datepicker/api#opt-headerText) - option
- [`open`](https://mobiscroll.com/docs/javascript/datepicker/api#method-open) - method
- [`inputElement`](https://mobiscroll.com/docs/javascript/select/api#opt-inputElement) - option
- [`touchUi`](https://mobiscroll.com/docs/javascript/select/api#opt-touchUi) - option
- [`onChange`](https://mobiscroll.com/docs/javascript/select/api#event-onChange) - event

## Code

### JS

```js
mobiscroll.setOptions({
  theme: 'ios',
  themeVariant: 'light'
});

var defaultEvents = [
  {
    id: 1,
    title: 'Office Tower HVAC System Overhaul',
    start: '2026-01-05T00:00',
    end: '2026-03-15T00:00',
    resource: 1,
    type: 'upgrade',
    clientGroup: 'Enterprise Solutions Group',
  },
  {
    id: 2,
    title: 'Executive Floor Climate Control Installation',
    start: '2026-01-10T00:00',
    end: '2026-03-20T00:00',
    resource: 1,
    type: 'installation',
    clientGroup: 'Enterprise Solutions Group',
  },
  {
    id: 3,
    title: 'Headquarters Heating System Maintenance',
    start: '2026-02-01T00:00',
    end: '2026-03-31T00:00',
    resource: 1,
    type: 'maintenance',
    clientGroup: 'Enterprise Solutions Group',
  },
  {
    id: 4,
    title: 'Building Infrastructure Assessment',
    start: '2026-01-15T00:00',
    end: '2026-03-25T00:00',
    resource: 2,
    type: 'inspection',
    clientGroup: 'Enterprise Solutions Group',
  },
  {
    id: 5,
    title: 'Campus Facilities Modernization',
    start: '2026-02-05T00:00',
    end: '2026-03-31T00:00',
    resource: 2,
    type: 'upgrade',
    clientGroup: 'Enterprise Solutions Group',
  },
  // Showing partial data. Download full source.
];

var assigneeResources = [
  {
    id: 1,
    name: 'Sarah Johnson',
    title: 'Senior HVAC Technician',
    color: '#4a7c9e',
    img: 'https://img.mobiscroll.com/demos/f1.png',
  },
  {
    id: 2,
    name: 'Mike Chen',
    title: 'Lead Facilities Engineer',
    color: '#7fa650',
    img: 'https://img.mobiscroll.com/demos/m1.png',
  },
  {
    id: 3,
    name: 'Emily Rodriguez',
    title: 'Electrical Systems Specialist',
    color: '#c76b8a',
    img: 'https://img.mobiscroll.com/demos/f2.png',
  },
  {
    id: 4,
    name: 'James Wilson',
    title: 'Master Electrician',
    color: '#4a9dad',
    img: 'https://img.mobiscroll.com/demos/m2.png',
  },
  {
    id: 5,
    name: 'Lisa Anderson',
    title: 'Building Automation Technician',
    color: '#d4a056',
    img: 'https://img.mobiscroll.com/demos/f3.png',
  },
  {
    id: 6,
    name: 'David Kim',
    title: 'HVAC Project Manager',
    color: '#5a9d76',
    img: 'https://img.mobiscroll.com/demos/m3.png',
  },
];

var typeResources = [
  {
    id: 'installation',
    name: 'installation',
    color: '#3b5998',
  },
  {
    id: 'maintenance',
    name: 'maintenance',
    color: '#2d7a4f',
  },
  {
    id: 'repair',
    name: 'repair',
    color: '#b8621b',
  },
  {
    id: 'inspection',
    name: 'inspection',
    color: '#6b4fa3',
  },
  {
    id: 'upgrade',
    name: 'upgrade',
    color: '#a03a3a',
  },
];

var groupedEvents = [];
var groupBy = 'assignee'; // 'assignee' or 'type'
var groupByClient = false;
var zoomLevel = 'month'; // 'quarter', 'month', 'week'
var rawEvents = defaultEvents.slice();
// Edit popup state
var editingEventId = null;

function groupEventsByClientQuarter(events) {
  var groups = {};
  var result = [];

  // Save old collapsed states including year and quarter
  var oldCollapsedStates = {};
  groupedEvents.forEach(function (ge) {
    var stateKey = ge.resource + '-' + ge.clientGroup + '-' + ge.year + '-' + ge.quarter;
    oldCollapsedStates[stateKey] = ge.collapsed;
  });

  // Group events by resource (assignee or type) + client + quarter
  events.forEach(function (event) {
    var resourceId = groupBy === 'assignee' ? event.resource : event.type;
    var eventStart = new Date(event.start);
    var month = eventStart.getMonth();
    var year = eventStart.getFullYear();
    var quarter = Math.floor(month / 3);
    var groupKey = resourceId + '-' + event.clientGroup + '-' + year + '-' + quarter;

    if (!groups[groupKey]) {
      groups[groupKey] = {
        resource: resourceId,
        clientGroup: event.clientGroup,
        year: year,
        quarter: quarter,
        events: [],
      };
    }

    groups[groupKey].events.push(event);
  });

  // Create grouped events
  Object.keys(groups).forEach(function (groupKey) {
    var groupData = groups[groupKey];
    var quarterEvents = groupData.events.sort(function (a, b) {
      return new Date(a.start).getTime() - new Date(b.start).getTime();
    });

    // Get color based on groupBy mode
    var color;
    if (groupBy === 'assignee') {
      var resourceItem = assigneeResources.find(function (r) {
        return r.id === groupData.resource;
      });
      color = resourceItem.color;
    } else {
      var typeObj = typeResources.find(function (r) {
        return r.id === groupData.resource;
      });
      color = typeObj.color;
    }

    var eventIds = quarterEvents
      .map(function (e) {
        return e.id;
      })
      .join('-');

    var earliestStart = quarterEvents[0].start;
    var latestEnd = quarterEvents.reduce(function (latest, event) {
      return new Date(event.end).getTime() > new Date(latest).getTime() ? event.end : latest;
    }, quarterEvents[0].end);

    var newId = 'group-' + groupKey + '-' + eventIds;

    // Use full key including year and quarter
    var stateKey = groupData.resource + '-' + groupData.clientGroup + '-' + groupData.year + '-' + groupData.quarter;
    var collapsedState = stateKey in oldCollapsedStates ? oldCollapsedStates[stateKey] : true;

    result.push({
      id: newId,
      title: groupData.clientGroup,
      resource: groupData.resource,
      clientGroup: groupData.clientGroup,
      year: groupData.year,
      quarter: groupData.quarter,
      start: earliestStart,
      end: latestEnd,
      color: color,
      count: quarterEvents.length,
      originalEvents: quarterEvents,
      collapsed: collapsedState,
    });
  });

  return result;
}

function prepareEventsForDisplay(events, colorByType) {
  return events.map(function (event) {
    return {
      id: event.id,
      title: event.title,
      start: event.start,
      end: event.end,
      resource: colorByType ? event.resource : event.type,
      type: event.type,
      assignee: event.resource,
      clientGroup: event.clientGroup,
      color: '#f8f9fa',
    };
  });
}

function updateView() {
  var currentResources = groupBy === 'assignee' ? assigneeResources : typeResources;
  var currentEvents;

  if (groupByClient) {
    groupedEvents = groupEventsByClientQuarter(rawEvents);
    currentEvents = groupedEvents;
  } else {
    groupedEvents = [];
    currentEvents = prepareEventsForDisplay(rawEvents, groupBy === 'assignee');
  }

  var timelineConfig;

  switch (zoomLevel) {
    case 'quarter':
      timelineConfig = { type: 'year', resolutionHorizontal: 'quarter', eventHeight: 'variable' };
      break;
    case 'month':
      timelineConfig = { type: 'year', resolutionHorizontal: 'month', eventHeight: 'variable' };
      break;
    case 'week':
      timelineConfig = { type: 'year', resolutionHorizontal: 'week', eventHeight: 'variable' };
      break;
  }

  calendar.setOptions({
    data: currentEvents,
    resources: currentResources,
    renderTimelineEvent: groupByClient ? renderGroupedEvent : renderSimpleEvent,
    view: { timeline: timelineConfig },
    dragBetweenResources: !groupByClient,
  });
}

function renderGroupedEvent(event) {
  var origEvent = event.original;
  var isExpanded = !origEvent.collapsed;

  // Get unique items (opposite of groupBy)
  var uniqueItems = {};
  origEvent.originalEvents.forEach(function (ev) {
    if (groupBy === 'assignee') {
      var typeObj = typeResources.find(function (r) {
        return r.id === ev.type;
      });
      if (typeObj) {
        uniqueItems[typeObj.id] = typeObj;
      }
    } else {
      var emp = assigneeResources.find(function (r) {
        return r.id === ev.resource;
      });
      if (emp) {
        uniqueItems[emp.id] = emp;
      }
    }
  });

  var itemCount = Object.keys(uniqueItems).length;
  var itemLabel = groupBy === 'assignee' ? 'type' : 'employee';

  // Generate expanded content HTML if expanded
  var expandedHTML = '';
  if (isExpanded) {
    var groupStart = new Date(origEvent.start).getTime();
    var groupEnd = new Date(origEvent.end).getTime();
    var groupDuration = groupEnd - groupStart;

    expandedHTML = origEvent.originalEvents
      .map(function (ev) {
        var evStart = new Date(ev.start).getTime();
        var evEnd = new Date(ev.end).getTime();
        var leftPercent = groupDuration > 0 ? ((evStart - groupStart) / groupDuration) * 100 : 0;
        var widthPercent = groupDuration > 0 ? ((evEnd - evStart) / groupDuration) * 100 : 100;

        var detailText = '';
        var typeDotColor = '';
        var avatarUrl = '';

        if (groupBy === 'assignee') {
          var typeObj = typeResources.find(function (r) {
            return r.id === ev.type;
          });
          if (typeObj) {
            detailText = typeObj.name;
            typeDotColor = typeObj.color;
          }
        } else {
          var employee = assigneeResources.find(function (r) {
            return r.id === ev.resource;
          });
          if (employee) {
            detailText = employee.name;
            avatarUrl = employee.img;
          }
        }

        return (
          '<div class="mds-event-group-original-event" title="' +
          ev.title +
          ', ' +
          mobiscroll.formatDate('MM/DD/YYYY', new Date(ev.start)) +
          ' - ' +
          mobiscroll.formatDate('MM/DD/YYYY', new Date(ev.end)) +
          '" style="margin-left:' +
          leftPercent +
          '%; width:' +
          widthPercent +
          '%;">' +
          '<div class="mbsc-flex mds-event-group-event-content">' +
          '<div class="mds-event-group-event-title mds-event-group-text-truncate">' +
          ev.title +
          '</div>' +
          '<div class="mbsc-flex mds-event-group-event-right">' +
          '<div class="mds-event-group-event-date mds-event-group-text-truncate">' +
          mobiscroll.formatDate('DD MMM', new Date(ev.start)) +
          ' - ' +
          mobiscroll.formatDate('DD MMM', new Date(ev.end)) +
          '</div>' +
          '<div class="mbsc-flex mds-event-group-event-detail">' +
          (avatarUrl ? '<img src="' + avatarUrl + '" alt="' + detailText + '" class="mds-event-group-event-avatar" />' : '') +
          (typeDotColor ? '<span class="mds-event-group-type-dot" style="background-color: ' + typeDotColor + '"></span>' : '') +
          '<div class="mds-event-group-event-info mds-event-group-text-truncate">' +
          detailText +
          '</div>' +
          '</div>' +
          '</div>' +
          '<div class="mds-event-group-edit-btn mbsc-flex mbsc-icon mbsc-font-icon mbsc-icon-pencil" data-event-id="' +
          ev.id +
          '"></div>' +
          '</div>' +
          '</div>'
        );
      })
      .join('');
  }

  return (
    '<div class="mbsc-flex mds-event-group-task mds-event-group-task-client' +
    (isExpanded ? ' expanded' : '') +
    '" style="border-left-color: ' +
    origEvent.color +
    '">' +
    '<div class="mbsc-flex mds-event-group-content">' +
    '<div class="mds-event-group-title-text mds-event-group-text-truncate">' +
    origEvent.clientGroup +
    '</div>' +
    '<div class="mbsc-flex mds-event-group-right">' +
    '<div class="mbsc-flex mds-event-group-meta">' +
    '<div class="mds-event-group-date-range">' +
    mobiscroll.formatDate('DD MMM', new Date(origEvent.start)) +
    ' - ' +
    mobiscroll.formatDate('DD MMM', new Date(origEvent.end)) +
    '</div>' +
    '<div class="mds-event-group-count">' +
    origEvent.count +
    ' task' +
    (origEvent.count > 1 ? 's' : '') +
    ', ' +
    itemCount +
    ' ' +
    itemLabel +
    (itemCount > 1 ? 's' : '') +
    '</div>' +
    '</div>' +
    '<div class="mbsc-flex mds-event-group-icon mbsc-icon mbsc-font-icon mbsc-icon-material-keyboard-arrow-down"></div>' +
    '</div>' +
    '</div>' +
    '<div class="mds-event-group-events"><div class="mds-event-group-events-inner">' +
    expandedHTML +
    '</div></div>' +
    '</div>'
  );
}

function renderSimpleEvent(event) {
  var origEvent = event.original;
  var detailText = '';
  var avatarUrl = '';
  var typeDotColor = '';

  if (groupBy === 'assignee') {
    // Show type with colored dot
    var typeObj = typeResources.find(function (t) {
      return t.id === origEvent.type;
    });
    if (typeObj) {
      detailText = typeObj.name;
      typeDotColor = typeObj.color;
    }
  } else {
    // Show assignee with avatar
    var employee = assigneeResources.find(function (r) {
      return r.id === origEvent.assignee;
    });
    if (employee) {
      detailText = employee.name;
      avatarUrl = employee.img;
    }
  }

  return (
    '<div class="mbsc-flex mds-event-simple">' +
    '<div class="mds-event-simple-title">' +
    '<div class="mds-event-simple-title-inner mds-event-group-text-truncate">' +
    origEvent.title +
    '</div>' +
    '</div>' +
    '<div class="mbsc-flex mds-event-simple-right">' +
    '<div class="mds-event-simple-date">' +
    mobiscroll.formatDate('DD MMM', new Date(origEvent.start)) +
    ' - ' +
    mobiscroll.formatDate('DD MMM', new Date(origEvent.end)) +
    '</div>' +
    (detailText
      ? '<div class="mbsc-flex mds-event-simple-subtitle-wrapper">' +
        (avatarUrl ? '<img src="' + avatarUrl + '" alt="' + detailText + '" class="mds-event-simple-avatar" />' : '') +
        (typeDotColor ? '<span class="mds-event-simple-type-dot" style="background-color: ' + typeDotColor + '"></span>' : '') +
        '<div class="mbsc-flex mds-event-simple-subtitle" style="' +
        (groupBy === 'assignee' ? '' : 'margin-left: 25px;') +
        '">' +
        detailText +
        '</div>' +
        '</div>'
      : '') +
    '</div>' +
    '</div>'
  );
}

var calendar = mobiscroll.eventcalendar('#demo-event-grouping', {
  dragToMove: true,
  dragToResize: true,
  dragToCreate: false,
  clickToCreate: false,
  dragBetweenResources: true,
  view: {
    timeline: {
      type: 'year',
      resolutionHorizontal: 'month',
      eventHeight: 'variable',
    },
  },
  data: defaultEvents,
  resources: assigneeResources,
  renderTimelineEvent: renderSimpleEvent,
  renderResource: function (resource) {
    if (groupBy === 'assignee') {
      // Employee resource
      return (
        '<div class="mbsc-flex">' +
        '<img alt="' +
        resource.name +
        '" class="mds-event-group-avatar" src="' +
        resource.img +
        '"/>' +
        '<div class="mds-event-group-cont">' +
        '<div class="mds-event-group-name">' +
        resource.name +
        '</div>' +
        '<div class="mds-event-group-title">' +
        resource.title +
        '</div>' +
        '</div>' +
        '</div>'
      );
    } else {
      // Type resource
      return (
        '<div class="mbsc-flex mds-event-group-type-resource">' +
        '<div class="mds-event-group-type-badge" style="background-color: ' +
        resource.color +
        '"></div>' +
        '<div class="mds-event-group-type-name">' +
        resource.name +
        '</div>' +
        '</div>'
      );
    }
  },
  renderHeader: function () {
    return (
      '<div mbsc-calendar-nav></div>' +
      '<div class="mbsc-flex mbsc-flex-1-0 mbsc-justify-content-end mds-event-group-header-controls">' +
      '<label>' +
      '<input mbsc-checkbox type="checkbox" id="group-by-client-quarter" data-theme="material" data-label="Group by Client/Quarter" />' +
      '</label>' +
      '<label>' +
      '<input mbsc-input id="event-grouping-input" class="mds-event-group-select" data-dropdown="true" data-input-style="box" />' +
      '</label>' +
      '<select id="group-by-select">' +
      '<option value="assignee" selected>View by Assignee</option>' +
      '<option value="type">View by Type</option>' +
      '</select>' +
      '</div>' +
      '<label>Quarterly<input mbsc-segmented type="radio" name="zoom-level" value="quarter"/></label>' +
      '<label>Monthly<input mbsc-segmented type="radio" name="zoom-level" value="month" checked/></label>' +
      '<label>Weekly<input mbsc-segmented type="radio" name="zoom-level" value="week"/></label>' +
      '<div mbsc-calendar-prev></div>' +
      '<div mbsc-calendar-today></div>' +
      '<div mbsc-calendar-next></div>'
    );
  },
  onEventUpdate: function (args) {
    var updatedEvent = args.event;
    var oldEvent = args.oldEvent;
    var newStart = new Date(updatedEvent.start).getTime();
    var newEnd = new Date(updatedEvent.end).getTime();

    if (groupByClient) {
      var oldStart = new Date(oldEvent.start).getTime();
      var oldEnd = new Date(oldEvent.end).getTime();
      var startDelta = newStart - oldStart;
      var endDelta = newEnd - oldEnd;

      // Nothing changed
      if (startDelta === 0 && endDelta === 0) return;

      var movedGroupedEvent = groupedEvents.find(function (ge) {
        return ge.id === oldEvent.id;
      });

      if (movedGroupedEvent) {
        var clientGroupName = movedGroupedEvent.clientGroup;
        var resourceId = movedGroupedEvent.resource;
        var wasCollapsed = movedGroupedEvent.collapsed;

        var isMove = startDelta === endDelta;

        var eventsToUpdate;

        if (isMove) {
          // MOVE: shift all original events by the same delta
          eventsToUpdate = movedGroupedEvent.originalEvents.map(function (originalEvent) {
            return {
              id: originalEvent.id,
              title: originalEvent.title,
              resource: originalEvent.resource,
              type: originalEvent.type,
              clientGroup: originalEvent.clientGroup,
              start: new Date(new Date(originalEvent.start).getTime() + startDelta),
              end: new Date(new Date(originalEvent.end).getTime() + startDelta),
            };
          });
        } else {
          // RESIZE: proportionally remap all child events within the new group span
          var oldGroupStart = oldStart;
          var oldGroupEnd = oldEnd;
          var oldGroupDuration = oldGroupEnd - oldGroupStart;
          var newGroupStart = newStart;
          var newGroupEnd = newEnd;
          var newGroupDuration = newGroupEnd - newGroupStart;

          eventsToUpdate = movedGroupedEvent.originalEvents.map(function (originalEvent) {
            var evStart = new Date(originalEvent.start).getTime();
            var evEnd = new Date(originalEvent.end).getTime();

            // Calculate relative positions (0 to 1) within the old group span
            var relativeStart = oldGroupDuration > 0 ? (evStart - oldGroupStart) / oldGroupDuration : 0;
            var relativeEnd = oldGroupDuration > 0 ? (evEnd - oldGroupStart) / oldGroupDuration : 1;

            // Map to the new group span
            var mappedStart = newGroupStart + relativeStart * newGroupDuration;
            var mappedEnd = newGroupStart + relativeEnd * newGroupDuration;

            // Ensure minimum duration for each child event
            var childDurationDays = (mappedEnd - mappedStart) / (1000 * 60 * 60 * 24);
            if (childDurationDays < 1) {
              mappedEnd = mappedStart + 1000 * 60 * 60 * 24; // At least 1 day
            }

            return {
              id: originalEvent.id,
              title: originalEvent.title,
              resource: originalEvent.resource,
              type: originalEvent.type,
              clientGroup: originalEvent.clientGroup,
              start: new Date(mappedStart),
              end: new Date(mappedEnd),
            };
          });
        }

        // Sync into rawEvents
        var updatedIds = {};
        eventsToUpdate.forEach(function (e) {
          updatedIds[e.id] = e;
        });
        rawEvents = rawEvents.map(function (e) {
          return updatedIds[e.id] ? updatedIds[e.id] : e;
        });

        // Rebuild grouped view from updated rawEvents
        updateView();

        // Restore collapsed state
        var newYear = new Date(eventsToUpdate[0].start).getFullYear();
        var newQuarter = Math.floor(new Date(eventsToUpdate[0].start).getMonth() / 3) + 1;

        var newGroupedEvent = groupedEvents.find(function (ge) {
          return ge.resource === resourceId && ge.clientGroup === clientGroupName && ge.year === newYear && ge.quarter === newQuarter;
        });

        if (newGroupedEvent) {
          newGroupedEvent.collapsed = wasCollapsed;
          calendar.setEvents(groupedEvents);
        }

        var actionLabel = isMove ? 'moved' : 'resized';
        mobiscroll.toast({
          message: eventsToUpdate.length + ' event(s) for ' + clientGroupName + ' have been ' + actionLabel + '.',
        });
      }
    } else {
      var oldResource = args.oldEvent.resource;
      var newResource = updatedEvent.resource;
      var resourceChanged = oldResource !== newResource;

      // Sync into rawEvents (dates + resource if changed)
      rawEvents = rawEvents.map(function (e) {
        if (e.id === updatedEvent.id) {
          var update = { start: updatedEvent.start, end: updatedEvent.end };
          if (resourceChanged) {
            if (groupBy === 'assignee') {
              update.resource = newResource;
            } else {
              update.type = newResource;
            }
          }
          return Object.assign({}, e, update);
        }
        return e;
      });

      if (resourceChanged) {
        var fromName;
        var toName;
        if (groupBy === 'assignee') {
          var fromRes = assigneeResources.find(function (r) {
            return r.id === oldResource;
          });
          var toRes = assigneeResources.find(function (r) {
            return r.id === newResource;
          });
          fromName = fromRes ? fromRes.name : oldResource;
          toName = toRes ? toRes.name : newResource;
        } else {
          fromName = oldResource;
          toName = newResource;
        }
        mobiscroll.toast({
          message: '"' + updatedEvent.title + '" moved from ' + fromName + ' to ' + toName + '.',
        });
      }
    }
  },
});

var editDatePicker = mobiscroll.datepicker('#event-grouping-dates', {
  controls: ['calendar'],
  select: 'range',
  display: 'center',
  touchUi: false,
  showRangeLabels: false,
  onChange: function (args) {
    var dates = args.value;
    var startVal = dates[0];
    var endVal = dates[1];

    if (editingEventId !== null && startVal && endVal) {
      var oldEvent = rawEvents.find(function (e) {
        return e.id === editingEventId;
      });

      if (!oldEvent) {
        return;
      }

      var eventTitle = oldEvent.title;
      var oldQuarter = Math.floor(new Date(oldEvent.start).getMonth() / 3);
      var newQuarter = Math.floor(new Date(startVal).getMonth() / 3);
      var oldYear = new Date(oldEvent.start).getFullYear();
      var newYear = new Date(startVal).getFullYear();
      var quarterChanged = groupByClient && (oldQuarter !== newQuarter || oldYear !== newYear);

      var applyUpdate = function () {
        rawEvents = rawEvents.map(function (e) {
          if (e.id === editingEventId) {
            return Object.assign({}, e, { start: startVal, end: endVal });
          }
          return e;
        });
        updateView();
        return true;
      };

      if (quarterChanged) {
        var quarterNames = ['Q1', 'Q2', 'Q3', 'Q4'];
        var fromLabel = quarterNames[oldQuarter] + ' ' + oldYear;
        var toLabel = quarterNames[newQuarter] + ' ' + newYear;

        mobiscroll.confirm({
          title: 'Move to different group',
          message: '"' + eventTitle + '" will move from ' + fromLabel + ' to ' + toLabel + '. Do you want to continue?',
          okText: 'Move',
          cancelText: 'Cancel',
          callback: function (result) {
            if (result) {
              applyUpdate();
              mobiscroll.toast({
                message: '"' + eventTitle + '" moved to ' + toLabel + '.',
              });
            }
          },
        });
      } else {
        if (applyUpdate()) {
          mobiscroll.toast({
            message: '"' + eventTitle + '" dates updated.',
          });
        }
      }
    }
  },
});

// Edit button click handler (on expanded subtasks)
document.addEventListener('click', function (event) {
  var editBtn = event.target.closest('.mds-event-group-edit-btn');
  if (editBtn) {
    event.stopPropagation();

    var eventId = Number(editBtn.getAttribute('data-event-id'));
    var rawEvent = rawEvents.find(function (e) {
      return e.id === eventId;
    });
    if (rawEvent) {
      editingEventId = eventId;
      editDatePicker.setOptions({ headerText: rawEvent.title });
      editDatePicker.setVal([new Date(rawEvent.start), new Date(rawEvent.end)]);
      editDatePicker.open();
    }
  }
});

mobiscroll.select('#group-by-select', {
  inputElement: document.getElementById('event-grouping-input'),
  touchUi: false,
  onChange: function (args) {
    groupBy = args.value;
    updateView();
  },
});

// Checkbox for client/quarter grouping
document.getElementById('group-by-client-quarter').addEventListener('change', function () {
  groupByClient = this.checked;
  updateView();
});

// Zoom level handler
document.addEventListener('change', function (event) {
  if (event.target && event.target.name === 'zoom-level') {
    zoomLevel = event.target.value;
    updateView();
  }
});

// Expand/collapse icon click handler
document.addEventListener('click', function (event) {
  if (event.target && event.target.classList.contains('mds-event-group-icon')) {
    event.stopPropagation();

    var task = event.target.closest('.mds-event-group-task');
    var eventEl = event.target.closest('.mbsc-schedule-event');
    var eventId = eventEl ? eventEl.getAttribute('data-id') : null;

    var groupedEvent = groupedEvents.find(function (e) {
      return e.id === eventId;
    });

    if (groupedEvent) {
      // Toggle collapsed state in data
      groupedEvent.collapsed = !groupedEvent.collapsed;

      // Toggle CSS class for animation
      if (task) {
        task.classList.toggle('expanded', !groupedEvent.collapsed);
      }

      // Refresh calendar after animation completes
      setTimeout(function () {
        calendar.refresh();
      }, 200);
    }
  }
});

updateView();
```

### HTML

```html
<div class="mds-event-group-calendar">
  <div id="demo-event-grouping"></div>
  <div id="event-grouping-dates"></div>
</div>
```

### CSS

```css
/* Calendar base styles */
.mds-event-group-calendar {
  height: 100%;
}
.mds-event-group-calendar .mbsc-timeline-row {
  height: 140px;
}
.mds-event-group-calendar .mbsc-timeline-resource-col {
  width: 240px;
}
.mds-event-group-calendar .mbsc-ios.mbsc-textfield-wrapper-box {
  margin: 10px 20px;
}
.mds-event-group-calendar .mbsc-timeline-resource-title {
  text-transform: capitalize;
}
/* Resource rendering - Employees */
.mds-event-group-avatar {
  width: 40px;
  height: 40px;
}
.mds-event-group-cont {
  padding: 0 7px;
}
.mds-event-group-name {
  font-size: 14px;
  line-height: 24px;
}
.mds-event-group-title {
  font-size: 12px;
  font-weight: 400;
  line-height: 16px;
}
/* Resource rendering - Types */
.mds-event-group-type-resource {
  align-items: center;
  padding: 8px 0;
}
.mds-event-group-type-badge {
  width: 12px;
  height: 12px;
  border-radius: 50%;
  margin: 0 10px;
}
.mds-event-group-type-name {
  font-size: 14px;
  font-weight: 600;
  line-height: 20px;
}
/* Enforce minimum event width so text is always visible */
.mds-event-group-calendar .mbsc-schedule-event {
  min-width: 72px;
}
.mds-event-group-calendar .mbsc-schedule-event:has(.mds-event-group-task-client) {
  min-width: 120px;
}
/* Grouped event - collapsed state */
.mds-event-group-task-client {
  background-color: #dddddd;
  border-left: 4px solid;
  border-radius: 0 8px 8px 0;
  box-shadow:
    0 2px 4px rgba(0, 0, 0, 0.12),
    0 1px 2px rgba(0, 0, 0, 0.08);
  flex-direction: column;
  container-type: inline-size;
  min-width: 120px;
}
/* Grouped event header content */
.mds-event-group-content {
  justify-content: space-between;
  align-items: center;
  padding: 10px 14px;
  height: 42px;
  box-sizing: border-box;
  gap: 8px;
}
/* Client group title */
.mds-event-group-title-text {
  font-size: 14px;
  font-weight: 600;
  color: #1e293b;
  line-height: 20px;
  min-width: 0;
  position: sticky;
  left: 250px;
}
/* Right side container (meta + icon) */
.mds-event-group-right {
  align-items: center;
  z-index: 1;
  background-color: #dddddd;
}
/* Meta information (dates + counts) */
.mds-event-group-meta {
  flex-direction: column;
  align-items: flex-end;
  flex: 1;
  margin: 0 12px;
}
.mds-event-group-date-range {
  color: #575757;
  font-size: 11px;
  margin-bottom: 2px;
}
.mds-event-group-count {
  font-size: 11px;
  white-space: nowrap;
}
/* Expand/collapse icon */
.mds-event-group-icon {
  font-size: 20px;
  cursor: pointer;
  transition: transform 0.2s ease;
  width: 24px;
  height: 24px;
  align-items: center;
  justify-content: center;
  transform: rotate(0deg);
}
/* Icon rotation when expanded */
.mds-event-group-task.expanded .mds-event-group-icon {
  transform: rotate(180deg);
}
/* Grid wrapper for smooth animation */
.mds-event-group-events {
  display: grid;
  grid-template-rows: 0fr;
  transition: grid-template-rows 0.2s ease;
}
.mds-event-group-events-inner {
  overflow: hidden;
  padding: 0 14px 4px;
  transition: padding 0.2s ease;
}
.mds-event-group-task.expanded .mds-event-group-events {
  grid-template-rows: 1fr;
}
/* Individual event in expanded list */
.mds-event-group-original-event {
  background: #f1f1f1;
  border-radius: 6px;
  margin-bottom: 6px;
  padding: 6px 10px;
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.14);
  box-sizing: border-box;
  min-height: 38px;
  min-width: 100px;
  overflow: hidden;
  container-type: inline-size;
}
@container (max-width: 180px) {
  .mds-event-group-meta { display: none; }
}
@container (max-width: 130px) {
  .mds-event-group-event-right { display: none; }
}
/* Event content layout */
.mds-event-group-event-content {
  justify-content: space-between;
  align-items: center;
  line-height: 14px;
}
/* Event title */
.mds-event-group-event-title {
  font-weight: 600;
  color: #1e293b;
  font-size: 13px;
  line-height: 18px;
  flex: 1;
  min-width: 30px;
  margin-right: 8px;
}
.mds-event-group-text-truncate {
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}
/* Right side (date + detail) */
.mds-event-group-event-right {
  flex-direction: column;
  align-items: flex-end;
  min-width: 0;
}
.mds-event-group-event-date {
  font-size: 11px;
  color: #94a3b8;
  text-align: right;
  margin-bottom: 2px;
  max-width: 100%;
}
/* Detail container (avatar/dot + text) */
.mds-event-group-event-detail {
  align-items: center;
  justify-content: flex-end;
  overflow: hidden;
  max-width: 100%;
}
.mds-event-group-event-info {
  font-size: 11px;
  font-weight: 700;
  color: #64748b;
  text-transform: capitalize;
}
/* Avatar for assignee in type view */
.mds-event-group-event-avatar {
  width: 16px;
  height: 16px;
  border-radius: 50%;
  margin-right: 6px;
}
/* Colored dot for type in assignee view */
.mds-event-group-type-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  margin-right: 6px;
}
/* Edit button on subtask events */
.mds-event-group-edit-btn {
  align-items: center;
  justify-content: center;
  font-size: 14px;
  cursor: pointer;
  color: #94a3b8;
  padding: 4px;
  margin-left: 8px;
  border-radius: 4px;
  transition: color 0.15s ease, background-color 0.15s ease;
  flex-shrink: 0;
}
.mds-event-group-edit-btn:hover {
  color: #1e293b;
  background-color: rgba(0, 0, 0, 0.06);
}
/* Simple event styling (no grouping) */
.mds-event-simple {
  padding: 10px 12px;
  border-radius: 6px;
  box-shadow:
    0 2px 4px rgba(0, 0, 0, 0.15),
    0 1px 2px rgba(0, 0, 0, 0.1);
  justify-content: space-between;
  align-items: center;
  height: 42px;
  box-sizing: border-box;
  color: #2c2c2c;
  background-color: #dddddd;
  container-type: inline-size;
  gap: 8px;
}
@container (max-width: 130px) {
  .mds-event-simple-right { display: none; }
}
/* Event title */
.mds-event-simple-title {
  font-size: 13px;
  font-weight: 600;
  position: sticky;
  left: 250px;
  min-width: 0;
}
.mds-event-simple-title-inner {
  display: inline-block;
  max-width: 100%;
}
/* Right side container */
.mds-event-simple-right {
  flex-direction: column;
  z-index: 1;
  background-color: #dddddd;
}
/* Date range */
.mds-event-simple-date {
  font-size: 11px;
  opacity: 0.85;
  white-space: nowrap;
  text-align: right;
  margin-bottom: 2px;
}
/* Subtitle wrapper (avatar/dot + text) */
.mds-event-simple-subtitle-wrapper {
  position: relative;
  align-items: center;
  justify-content: flex-end;
}
/* Avatar for assignee in type view */
.mds-event-simple-avatar {
  width: 20px;
  height: 20px;
  border-radius: 50%;
  margin-right: 6px;
  position: absolute;
  left: 0;
}
/* Colored dot for type in assignee view */
.mds-event-simple-type-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  margin: 0 6px;
}
/* Subtitle text (type or assignee name) */
.mds-event-simple-subtitle {
  font-size: 11px;
  font-weight: 700;
  text-transform: capitalize;
  white-space: nowrap;
}
/* Header controls */
.mds-event-group-header-controls {
  align-items: center;
}
/* Select input */
.mds-event-group-select.mbsc-textfield {
  width: 210px;
  max-height: 34px;
}
.mds-event-group-select + .mbsc-ios.mbsc-select-icon {
  font-size: 13px;
  top: 8px;
}
.mds-event-group-calendar .mbsc-ios.mbsc-segmented-button {
  padding: 1px 12px;
}
```

## Implementation notes

- Use `type: 'year'` with `resolutionHorizontal` driven by a `zoomLevel` state (values: `'quarter'`, `'month'`, `'week'`) and `eventHeight: 'variable'` to accommodate collapsible grouped event blocks.
- Define two separate resource arrays: `assigneeResources` (employees with `name`, `title`, `color`, `img`) and `typeResources` (work categories with `name`, `color`). Keep a `groupBy` state (`'assignee'` or `'type'`) and pass the matching array to `resources`. When `groupBy` is `'type'`, the event's `type` field is used as the `resource` key; when `'assignee'`, the `resource` field is used.
- Keep a `groupByClientQuarter` boolean toggle state. When disabled, map each event to a display-ready object with the correct resource key for the current `groupBy` mode. When enabled, compute grouped events instead.
- To compute grouped events, group the flat event array by `(resourceId, clientGroup, year, quarter)`. For each group, create a synthetic event object with a `title` (client name), a `start` (earliest start), an `end` (latest end), a `count`, an `originalEvents` array, and a `collapsed` flag read from a `collapsedMap` state (defaulting to `true`).
- Use `renderTimelineEvent` (Angular: `timelineEventTemplate`, Vue: `#timelineEvent` slot) for event rendering. When `groupByClientQuarter` is on, render the grouped block; when off, render a simple individual event with the event title, date range, and either a type color dot or an assignee avatar.
- The grouped event block shows the client group name, a formatted date range, a task count and unique type/employee count, and a collapse/expand arrow button. When expanded, render each original event as a proportional mini bar positioned by its relative offset within the group's time span using computed `marginLeft` and `width` percentages.
- On the collapse arrow click, call `stopPropagation`, toggle the group's key in `collapsedMap`, and call `calendarRef.current.refresh()` after a short timeout to force Mobiscroll to recalculate event heights.
- Each expanded original event has a pencil icon button. On click, call `stopPropagation` and open a `Datepicker` in `select: 'range'` and `controls: ['calendar']` mode centered on screen, pre-populated with the event's current dates.
- In the `Datepicker` `onChange` handler, if the new dates move the event to a different quarter and grouping is on, show a `Confirm` dialog before applying. Store the apply callback in a ref so the `onOk` handler can execute it after the user confirms.
- In `onEventUpdate`, distinguish drag-move from drag-resize by comparing start and end deltas. For a grouped event move, shift all `originalEvents` by the same time delta. For a resize, proportionally remap each child's start and end within the new group span. After applying, update the `collapsedMap` with a new key reflecting the event's new quarter. In non-grouped mode, update the single event's dates and, if the resource row changed, update the event's `resource` or `type` field accordingly.
- Set `dragBetweenResources` to `true` in non-grouped mode and `false` in grouped mode (a single expression: `!groupByClientQuarter`). Keep `dragToMove: true` and `dragToResize: true`; disable `clickToCreate` and `dragToCreate`.
- Use `renderResource` (Angular: `resourceTemplate`, Vue: `#resource` slot) to show a photo, name, and title for assignee resources, and a colored badge with name for type resources.
- Use `renderHeader` (Angular: `headerTemplate`, Vue: `#header` slot) to render `CalendarNav`, a `Checkbox` for the group toggle, a `Select` for switching between assignee and type views, a `SegmentedGroup` with three `Segmented` controls for zoom level, and `CalendarPrev`/`CalendarToday`/`CalendarNext`.

## Run it in your project

1. If not signed up yet, or don't own a license, you can [start a free trial](https://mobiscroll.com/starttrial).

2. Clone the repository:

   ```
   git clone https://github.com/acidb/mobiscroll-demos-javascript.git
   ```

3. If not installed yet, install the Mobiscroll CLI from NPM:

   ```
   npm install -g @mobiscroll/cli
   ```

4. Config Mobiscroll - open a terminal window in the root directory and run:

   ```
   mobiscroll config javascript
   ```

5. Install dependencies - open a terminal window in the root directory and run:

   ```
   npm install
   ```

6. Run the project:

   ```
   npm run dev
   ```

On a trial, add `--trial` to the config command: `mobiscroll config javascript --trial`.

Running a demo locally requires a Mobiscroll trial or a license; setup is per framework at https://mobiscroll.com/docs/javascript/getting-started/installation

## Related demos

- Previous: [External Resource Drag & Drop](https://demo.mobiscroll.com/javascript/timeline/resource-management-with-dynamic-team-creation.md) - Drag external resources onto a Javascript Timeline to add team members, or drag them off to remove them — build crew scheduling and team management.
- Next: [36-Hour Rolling Window Schedule](https://demo.mobiscroll.com/javascript/timeline/36-hour-rolling-window-aircraft-view.md) - Build a fleet scheduling view on the Javascript Timeline — a 36-hour rolling window that auto-advances from the current hour.