How-tos

How to toggle grid/chart

If you use the default layout configuration, you can change the show_grid or show_chart parameters and use the render() method to repaint the changes.

function toggleGrid(){
    gantt.config.show_grid = !gantt.config.show_grid;
    gantt.render();
}

function toggleChart(){
    gantt.config.show_chart = !gantt.config.show_chart;
    gantt.render();
}

If you use a custom layout configuration, you need to create several layout configurations - with and without a grid/timeline. To switch between them, you need to modify the gantt.config.layout parameter and apply the init() method to see the changes:

let showGrid = true;
function toggleGrid() {
    showGrid = !showGrid;
    if (showGrid) {
        gantt.config.layout = gridAndChart; // layout with grid and timeline
    }
    else {
        gantt.config.layout = onlyChart; // layout with the timeline only
 
    }
    gantt.init("gantt_here");
}

let showChart = true;
function toggleChart() {
    showChart = !showChart;
    if (showChart) {
        gantt.config.layout = gridAndChart; // layout with grid and timeline
    }
    else {
        gantt.config.layout = onlyGrid; // layout with the grid only
 
    }
    gantt.init("gantt_here");
}

How to toggle the resource view

As with the previous use case, you need to create several layout configurations - with and without resource views. To switch between them, you need to modify the gantt.config.layout parameter and apply the init() method to see the changes:

let resourceChart = true;
 
function layoutChange() {
    resourceChart = !resourceChart;
    if (resourceChart) {
        gantt.config.layout = resourceLayout;
    }
    else {
        gantt.config.layout = noresourceLayout;
    }
    gantt.init("gantt_here");
};

let histogramView = true;
 
function layoutChange() {
    histogramView = !histogramView;
    if (histogramView) {
        gantt.config.layout = histogramLayout;
    }
    else {
        gantt.config.layout = simpleLayout;
    }
    gantt.init("gantt_here");
};

Alternatively, you can generate layout by using the layout views and re-initializing Gantt to see the changes:

Related sample: Gantt. Generate layout

How to have an infinite scroll in the timeline

There are several ways to implement an infinite scroll. But in most cases, you will need to modify the displayed date range (gantt.config.start_date and gantt.config.end_date parameters):

While using the scrollbar

You need to obtain the scroll position and increase the date range. Note, repainting of Gantt too often will affect performance, therefore you will need to do that after a timeout:

gantt.init("gantt_here");
gantt.parse(tasks);
 
gantt.attachEvent("onGanttScroll", function (left, top) {
    const left_date = gantt.dateFromPos(left)
    const right_date = gantt.dateFromPos(left + gantt.$task.offsetWidth)
 
    gantt.config.start_date = gantt.config.start_date || gantt.getState().min_date;
    gantt.config.end_date = gantt.config.end_date || gantt.getState().max_date;
 
    const min_allowed_date = gantt.date.add(gantt.config.start_date, 1, "day");
    const max_allowed_date = gantt.date.add(gantt.config.end_date, -2, "day");
 
    let repaint = false;
    if (+left_date <= +min_allowed_date) {
        gantt.config.start_date = gantt.date.add(gantt.config.start_date, -2, "day");
        repaint = true;
    }
    if (+right_date >= +max_allowed_date) {
        gantt.config.end_date = gantt.date.add(gantt.config.end_date, 2, "day");
        repaint = true;
    }
 
    if (repaint) {
        setTimeout(function () {
            gantt.render()
            gantt.showDate(left_date)
        }, 20)
    }
});

While dragging the timeline

You need to get the current scroll position and if it is near the start or end of the timeline, increase the displayed date range:

gantt.attachEvent("onMouseMove", function (id, e) {
  if (!gantt.getState().drag_id && e.buttons == 1) {
    const left_date = gantt.dateFromPos(gantt.getScrollState().x);
    const right_date = gantt.dateFromPos(
      gantt.getScrollState().x + gantt.$task.offsetWidth - 1
    );
    if (left_date && +left_date <= +gantt.config.start_date) {
      gantt.config.start_date = gantt.date.add(gantt.config.start_date, -1, 'day');
      gantt.render();
    }
    if (right_date && +gantt.config.end_date < +gantt.date.add(right_date, 1, 'day')) {
      gantt.config.end_date = gantt.date.add(gantt.config.end_date, 1, 'day');
      gantt.render();
    }
  }
});

While dragging a task

If the date range is not set, you can call the render() method each time the task is dragged near the start or end of the timeline:

gantt.init("gantt_here");
gantt.parse(tasks);
 
gantt.attachEvent("onTaskDrag", function (id, mode, task, original) {
    if (task.start_date <= gantt.getState().min_date ||
        task.end_date >= gantt.getState().max_date) {
        gantt.render()
    }
});

If the date range is set, you will need to modify it:

gantt.init("gantt_here");
gantt.parse(tasks);
 
gantt.config.start_date = new Date(2025, 02, 28)
gantt.config.end_date = new Date(2025, 03, 10)
gantt.render();
 
gantt.attachEvent("onTaskDrag", function (id, mode, task, original) {
    if (+task.start_date <= +gantt.config.start_date) {
        gantt.config.start_date = gantt.date.add(
            gantt.config.start_date, -1, gantt.config.duration_unit
        );
        gantt.render()
    }
    if (+task.end_date >= +gantt.config.end_date) {
        gantt.config.end_date = gantt.date.add(
            gantt.config.end_date, 1, gantt.config.duration_unit
        );
        gantt.render()
    }
});

How to load tasks dynamically

You can detect that you have scrolled to the last visible task in the onGanttScroll event and use the parse() method to load new tasks:

gantt.attachEvent("onGanttScroll", function (left, top) {
    const visibleTasks = gantt.getVisibleTaskCount();
    const lastVisibleTask = gantt.getTaskByIndex(visibleTasks - 1)
 
    if (gantt.getTaskRowNode(lastVisibleTask.id)) {
        const tasks = load_tasks()
        gantt.parse(tasks);
    }
});

How to expand/collapse all tasks with a button

You can use the open() and close() methods to open and close a task. To do that with all tasks in the chart, you need to use the method inside the eachTask() function. To repaint the changes only once, you can wrap the function with the batchUpdate() method:

function collapseAll() {
    gantt.batchUpdate(function () {
        gantt.eachTask(function (task) {
            gantt.close(task.id)
        })
    })
}
 
function expandAll() {
    gantt.batchUpdate(function () {
        gantt.eachTask(function (task) {
            gantt.open(task.id)
        })
    })
}

How to display several lines in the grid cell/header

This can be achieved by adding some style rules.

For the grid header:

.gantt_grid_head_text{
    line-height: 12px;
    white-space:normal;
}

For the grid cells:

.gantt_tree_content, .gantt_task_content{
    line-height: 12px;
    white-space:normal;
    overflow-wrap: break-word; 
}

How to add a custom column in the grid

To add a custom column, you need to modify the gantt.config.columns parameter. If you specify the name parameter, Gantt will return the value of the task property with the same name. You can also use the template() function to return any custom date or HTML elements.

gantt.config.columns = [
    /*
    other columns
    */
    {
        name: "progress", label: "Progress", width: 50, resize: true, align: "center", 
        template: function (task) {
            return Math.round(task.progress * 100) + "%"
        }
    },
    /*
    other columns
    */
];

How to add a custom add(+) button

You need to create a custom column via the gantt.config.columns parameter. You can set any name for that column except add. Otherwise, Gantt will add the default add column. It is possible to return any HTML elements in the grid column by using the template function. It means that you can return a button and attach a click event to it with a custom function for adding tasks.

gantt.config.columns = [
    /*
    other columns
    */
    {
        name: "add_tasks", label: "+", width: 50, resize: true, align: "center", 
        template: function (task) {
            return `<button onclick='addTask(${task.id})';>`
        }
    },
];

How to add a custom scale

You need to create a custom scale unit and add logic to calculate the dates.

An example of a custom scale with work shift hours (06:30, 18:30):

gantt.date.custom_scale_start = function (date) {
    return date;
};
 
gantt.date.add_custom_scale = function (date, inc) {
    let next = new Date(date)
    if (!next.getMinutes()) {
        gantt.date.day_start(next)
        next = gantt.date.add(next, 6, "hour");
        next = gantt.date.add(next, 30, "minute");
    }
    else {
        next = gantt.date.add(next, 12 * inc, "hour");
    }
    return next
};
 
gantt.config.scales = [
    { unit: "day", step: 1, date: "%d" },
    { unit: "custom_scale", step: 1, date: "%H:%i" },
];

An example of a custom scale with numbers instead of days:

gantt.config.scales = [
    {
        unit: "day", step: 1, format: function (date) {
            return gantt.getScale().trace_indexes[+date] + 1
        }
    }
]

An example of a custom scale with 5-day work weeks:

const weekScaleTemplate = function (date) {
    const dateToStr = gantt.date.date_to_str("%d");
    const endDate = gantt.date.add(gantt.date.add(date, 5, "day"), -1, "day");
    return dateToStr(date) + " - " + dateToStr(endDate);
};
 
gantt.date.five_days_start = function (date) {
    return date;
};
 
gantt.date.add_five_days = function (date, inc) {
    if (date.getDay() == 0 || date.getDay() == 6) {
        return gantt.date.add(date, 1 * inc, "day");
    }
    gantt.date.week_start(date);
    return gantt.date.add(date, 5 * inc, "day");
};
 
 
gantt.config.scales = [
    { unit: "month", step: 1, format: "%F, %Y" },
    { unit: "five_days", step: 1, format: weekScaleTemplate },
];
 
gantt.ignore_time = function (date) {
    return date.getDay() == 0 || date.getDay() == 6;
};

An example of a custom scale with weeks of the year (the week's number starts from the first day of the year):

gantt.date.custom_week_start = function (date) {
    return date;
};
 
gantt.date.add_custom_week = function (date, inc) {
    const year_start = new Date(date);
    gantt.date.year_start(year_start);
    const week_number = Math.round(gantt.calculateDuration(year_start, date) / 7);
 
    const next_week = gantt.date.add(year_start, week_number + 1, "week");
    if (next_week.getYear() != date.getYear()) {
        gantt.date.year_start(next_week)
    }
    return next_week;
};
 
 
const custom_week_template = function (date) {
    const year_start = gantt.date.year_start(new Date(date));
    const week_number = Math.round(gantt.calculateDuration(year_start, date) / 7) + 1;
 
    return "Week:" + week_number
}
 
gantt.config.scales = [
    { unit: 'custom_week', step: 1, template: custom_week_template },
    { unit: 'day', step: 1, format: "%d, %M" },
];

How to copy and paste tasks

You can use the copy() method to create a deep copy of the task object. Then, you can change the ID of the cloned task. After that, you can add the cloned task with the addTask() or createTask() methods.

This is how you can add a button to clone a task:

function clone_task(id) {
    const task = gantt.getTask(id);
    const clone = gantt.copy(task);
    clone.id = +(new Date());
    gantt.addTask(clone, clone.parent, clone.$index)
}
 
gantt.config.columns = [
    /*
    other columns
    */
    {
        name: "clone", label: "clone", width: 44, template: function (task) {
            return "<input type=button value='V' onclick=clone_task(" + task.id + ")>"
        }
    }
];

Related sample: Gantt. Clone a task

The following example shows how to clone a task with all its subtasks and links:

let child_links;
let clone_original_ids_table;
 
function obtain_link_ids(id) {
  const task = gantt.getTask(id);
  const source_links = task.$source;
  for (let i = 0; i < source_links.length; i++) {
    child_links.push(source_links[i]);
  }
}
 
function create_clone_original_ids_table(original_id, clone_id) {
  clone_original_ids_table[original_id] = clone_id;
}
 
function clone_child_links() {
 for (let i = 0; i < child_links.length; i++) {
  const link = gantt.getLink(child_links[i]);
  if (clone_original_ids_table[link.source] && clone_original_ids_table[link.target]){
    const clone_link = {};
    clone_link.id = gantt.uid();
    clone_link.target = clone_original_ids_table[link.target];
    clone_link.source = clone_original_ids_table[link.source];
    clone_link.type = link.type;
    gantt.addLink(clone_link)
  }
 }
}
 
function clone_children(id, new_parent) {
  const children = gantt.getChildren(id)
  for (let i = 0; i < children.length; i++) {
    const child_original = gantt.getTask(children[i]);
    const child_clone = gantt.copy(child_original);
    child_clone.id = gantt.uid();
    child_clone.parent = new_parent;
    gantt.addTask(child_clone, child_clone.parent, child_clone.$index);
 
    obtain_link_ids(child_original.id);
    create_clone_original_ids_table(child_original.id, child_clone.id);
 
    if (gantt.hasChild(child_original.id)) clone_children(
      child_original.id, child_clone.id
    );
  }
}
 
function clone_task(id) {
  const task = gantt.getTask(id);
  const clone = gantt.copy(task);
  clone.id = gantt.uid();
  gantt.addTask(clone, clone.parent, clone.$index);
 
  child_links = [];
  obtain_link_ids(id);
 
  clone_original_ids_table = {};
  create_clone_original_ids_table(task.id, clone.id);
 
  if (gantt.hasChild(id)) {
    clone_children(id, clone.id)
  }
 
  clone_child_links()
}
 
gantt.config.order_branch = true;
gantt.config.order_branch_free = true;
 
gantt.config.columns = [
  /*
  other columns
  */
  {
    name: "clone", label: "clone", width: 44, template: function (task) {
      return "<input type=button value='V' onclick=clone_task(" + task.id + ")>"
    }
  }
];

One more example demonstrates how to implement copying via key navigation (select tasks, use the Ctrl + C hotkey to copy them, and Ctrl + V hotkey to paste them as children to the selected task):

gantt.plugins({
    keyboard_navigation: true,
    multiselect: true,
})
 
let tasks_to_copy = [];
 
gantt.ext.keyboardNavigation.addShortcut("ctrl+c", function (e) {
    tasks_to_copy = [];
    gantt.eachSelectedTask(function (task_id) {
        tasks_to_copy.push(task_id);
    });
}, "taskRow");
gantt.ext.keyboardNavigation.addShortcut("ctrl+v", function (e) {
    const new_parent = gantt.getSelectedId();
    for (let i = 0; i < tasks_to_copy.length; i++) {
        const task = gantt.copy(gantt.getTask(tasks_to_copy[i]));
        task.id = +new Date() + '+' + Math.floor(Math.random() * 10);
        gantt.addTask(task, new_parent)
    }
    gantt.getTask(new_parent).$open = true;
    gantt.render()
}, "taskRow");

How to add resource chart or custom styles in the exported PDF file

You need to export the data in the raw mode and include the styles in the header or footer parameters of the export function.

For example, you can save custom styles in a variable and then add the variable to the header parameter

const header = `
    .gantt_bar_task {
        background: orange;
    }
 
    .gantt_task_progress {
        background-color: rgba(33, 33, 33, 0.17);
    }
`
 
gantt.exportToPDF({
       header: "<style>" + header + "</style>"
});

Or you can find the <style> element on the page and add its content as in:

gantt.exportToPDF({
    raw: true,
    header: "<style>" + document.getElementById("styles").innerHTML + "</style>"
});
 
<style id='styles'>
    .gantt_bar_task {
        background: orange;
    }
 
    .gantt_task_progress {
        background-color: rgba(33, 33, 33, 0.17);
    }
</style>

An example of exporting Gantt with legend:

Examples of exporting resource load diagram and histogram:

How to calculate task progress depending on child tasks

A simple way to implement that is calculate the progress of a parent task after you update a child task. To iterate over parent tasks, you can use the eachParent() method.

In the following example, the progress of parent tasks depends only on the progress of child tasks:

gantt.config.auto_types = true;
 
gantt.templates.progress_text = function (start, end, task) {
    return "<span style='text-align:left;'>" + Math.round(task.progress * 100) 
          + "% </span>";
};
 
gantt.init("gantt_here");
gantt.parse({
    "data": [
        ...
    ]
});
 
gantt.attachEvent("onAfterTaskUpdate", function (id, task) {
    parentProgress(id)
});
gantt.attachEvent("onTaskDrag", function (id, mode, task, original) {
    if (mode == "progress") {
        parentProgress(id)
    }
});
gantt.attachEvent("onAfterTaskAdd", function (id) {
    parentProgress(id)
});
gantt.attachEvent("onAfterTaskDelete", function (id, task) {
    if (task.parent) {
        const siblings = gantt.getChildren(task.parent);
        if (siblings.length) {
            parentProgress(siblings[0])
        }
    }
});
 
function parentProgress(id) {
    gantt.eachParent(function (task) {
        const children = gantt.getChildren(task.id);
        let childProgress = 0;
        for (let i = 0; i < children.length; i++) {
            const child = gantt.getTask(children[i])
            childProgress += (child.progress * 100);
        }
        task.progress = childProgress / children.length / 100;
    }, id)
    gantt.render();
}

In the next example, the progress of parent tasks depends on the progress of child tasks and their duration:

function calculateSummaryProgress(task) {
    if (task.type != gantt.config.types.project)
        return task.progress;
    var totalToDo = 0;
    var totalDone = 0;
    gantt.eachTask(function (child) {
        if (child.type != gantt.config.types.project) {
            totalToDo += child.duration;
            totalDone += (child.progress || 0) * child.duration;
        }
    }, task.id);
    if (!totalToDo) return 0;
    else return totalDone / totalToDo;
}
 
function refreshSummaryProgress(id, submit) {
    if (!gantt.isTaskExists(id))
        return;
 
    var task = gantt.getTask(id);
    var newProgress = calculateSummaryProgress(task);
 
    if (newProgress !== task.progress) {
        task.progress = newProgress;
 
        if (!submit) {
            gantt.refreshTask(id);
        } else {
            gantt.updateTask(id);
        }
    }
 
    if (!submit && gantt.getParent(id) !== gantt.config.root_id) {
        refreshSummaryProgress(gantt.getParent(id), submit);
    }
}
 
 
gantt.attachEvent("onParse", function () {
    gantt.eachTask(function (task) {
        task.progress = calculateSummaryProgress(task);
    });
});
 
gantt.attachEvent("onAfterTaskUpdate", function (id) {
    refreshSummaryProgress(gantt.getParent(id), true);
});
 
gantt.attachEvent("onTaskDrag", function (id) {
    refreshSummaryProgress(gantt.getParent(id), false);
});
gantt.attachEvent("onAfterTaskAdd", function (id) {
    refreshSummaryProgress(gantt.getParent(id), true);
});
 
 
(function () {
    var idParentBeforeDeleteTask = 0;
    gantt.attachEvent("onBeforeTaskDelete", function (id) {
        idParentBeforeDeleteTask = gantt.getParent(id);
    });
    gantt.attachEvent("onAfterTaskDelete", function () {
        refreshSummaryProgress(idParentBeforeDeleteTask, true);
    });
})();
 
...
 
gantt.config.auto_types = true;
 
gantt.templates.progress_text = function (start, end, task) {
    return "<span style='text-align:left;'>" + Math.round(task.progress * 100) 
          + "% </span>";
};
 
gantt.templates.task_class = function (start, end, task) {
    if (task.type == gantt.config.types.project)
        return "hide_project_progress_drag";
};

How to vertically reorder tasks in the timeline

You can use the addTaskLayer() method to display custom HTML elements in the timeline and add functions to drag them vertically and horizontally.

In the following example, it will work as a regular task reorder in the grid:

In the following example, you can reorder split tasks and place tasks on the same row:

How to freeze/fix columns in the grid

This can be done by using CSS. You need to set the 'relative' position to the column that needs to be fixed. The 'left' parameter should have the same value as the scrollbar position, so, you can add the event handler to the scrollbar and update the CSS variable:

gantt.attachEvent("onGanttReady", function () {
    const el = document.querySelector(".gantt_hor_scroll");
    if (el) {
        el.addEventListener('scroll', function () {
            document.documentElement.style.setProperty(
              '--gantt-frozen-column-scroll-left', el.scrollLeft + "px"
            );
        });
    }
});
 
const textEditor = { type: "text", map_to: "text" };
const start_dateEditor = { type: "date", map_to: "start_date" };
const end_dateEditor = { type: "date", map_to: "end_date" };
const durationEditor = { type: "number", map_to: "duration", min: 0, max: 100 };
 
 
gantt.config.columns = [
    { name: "text", tree: true, width: 150, resize: true, editor: textEditor },
    { name: "start_date", align: "center", width: 120, resize: true, 
      editor: start_dateEditor },
    { name: "end_date", label: "End Time", align: "center", width: 120, 
      resize: true, editor: end_dateEditor },
    { name: "duration", align: "center", width: 80, resize: true, 
      editor: durationEditor },
    { name: "progress", label: "Progress", width: 80, align: "center", 
      resize: true },
    {
        name: "custom", label: "Custom", width: 180, align: "center", 
        resize: true, template: function (task) {
            return Math.round(Math.random() * 100)
        }
    },
    { name: "add", width: 44 }
];
 
gantt.config.layout = {
    css: "gantt_container",
    cols: [
        {
            rows: [
                {
                    view: "grid", scrollable: true, 
                    scrollX: "scrollHor1", scrollY: "scrollVer"
                },
                {
                    view: "scrollbar", id: "scrollHor1",
                    scroll: 'x', group: 'hor'
                },
            ]
        },
        { resizer: true, width: 1 },
        {
            rows: [
                {
                    view: "timeline", scrollX: "scrollHor", scrollY: "scrollVer"
                },
                {
                    view: "scrollbar", id: "scrollHor",
                    scroll: 'x', group: 'hor'
                },
            ]
        },
        { view: "scrollbar", id: "scrollVer" }
    ]
}

And add CSS styles:

:root {
    --gantt-frozen-column-scroll-left: 0px;
}
 
.gantt_cell:nth-child(1),
.gantt_grid_head_cell:nth-child(1) {
    background: Azure;
    position: relative;
    left: var(--gantt-frozen-column-scroll-left);
}
 
.gantt_grid_editor_placeholder[data-column-name="text"] {
    left: var(--gantt-frozen-column-scroll-left) !important;
}
 
.gantt_grid_head_cell:nth-child(1) {
    z-index: 1;
}

Another way is to add several grid views, but it doesn't work well with the inline editors:

gantt.config.columns = [
    { name: "start_date", align: "center", width: 80, resize: true },
    { name: "end_date", label: "End Date", align: "center", width: 80, resize: true },
    { name: "duration", width: 60, align: "center", resize: true },
    { name: "progress", label: "Progress", width: 60, align: "center", resize: true },
    { name: "add", width: 44 }
];
 
 
const fixedColumn = {
    columns: [
        { name: "text", tree: true, width: 200, resize: true },
    ]
};
 
gantt.config.layout = {
  css: "gantt_container",
  cols: [
    {
      width: 400,
      //min_width: 100,
      rows: [
        {
          group: "gantt",
          cols: [
            {
              rows: [
                { view: 'grid', config: fixedColumn, bind: "task", 
                  scrollY: 'gridScrollY' }
              ]
            },
            {
              rows: [
                { view: 'grid', bind: "task", scrollX: 'gridScrollX', 
                  scrollable: true, scrollY: 'gridScrollY' },
                { view: 'scrollbar', id: 'gridScrollX' }
              ]
            },
            { view: 'scrollbar', id: 'gridScrollY' }
          ]
        }
      ]
    },
    { resizer: true, width: 1 },
    {
      rows: [
        {
          group: "gantt",
          cols: [
            {
              rows: [
                { view: "timeline", scrollX: "scrollHor", scrollY: "scrollVer" },
                { view: "scrollbar", id: "scrollHor" }
              ]
            },
            { view: 'scrollbar', id: 'scrollVer' }
          ]
        }
      ]
    }
  ]
}

How to add legend to the gantt

There is no built-in method for displaying legend in the Gantt, the closest thing is the Overlay extension, but it’s not exactly the same and can’t be customized that easily.

However, legends can be implemented fairly simple. You can code the legend element in HTML and then just inject it into the gantt node:

gantt.$root.appendChild(legend);

Here is a live example, to show the legend, press the "Toggle legend" button on top of the gantt:

To add interactivity, you can add listeners for DOM events to the legend element directly, or you can listen to DOM events at the root level of the gantt (event delegation):

gantt.event(gantt.$root, "click", function(e){
    var closest = gantt.utils.dom.closest;
    if(closest(e.target, ".gantt-legend")) {
        gantt.message("Mouse click inside the legend element");
    }
});