Task dependency in EJ2 JavaScript Gantt control

17 Aug 202324 minutes to read

Task dependency or task relationship can be established between two tasks in Gantt. This dependency affects the project schedule. If you change the predecessor of a task, it will affect the successor task, which will affect the next task, and so on. Relationship can be established between parent-parent tasks, child-child tasks, parent-child and child-parent task.

In Gantt, you can enable or disable the parent predecessor using allowParentDependency property.

By default, the allowParentDependency property will be true.

Task relationship types

Task relationships are categorized into four types based on the start and finish dates of the task.

Start to Start (SS)

You cannot start a task until the dependent task also starts.

Alt text

Start to Finish (SF)

You cannot finish a task until the dependent task is started.

Alt text

Finish to Start (FS)

You cannot start a task until the dependent task is completed.

Alt text

Finish to Finish (FF)

You cannot finish a task until the dependent task is completed.

Alt text

Define task relationship

Task relationship is defined in the data source as a string value, and this value is mapped to the Gantt control by using the taskFields.dependency property. The following code example demonstrates how to enable the predecessor in the Gantt control.

var GanttData = [
        {
            TaskID: 1,
            TaskName: 'Project Initiation',
            StartDate: new Date('04/02/2019'),
            EndDate: new Date('04/21/2019'),
            subtasks: [
                { TaskID: 2, TaskName: 'Identify Site location', StartDate: new Date('04/02/2019'), Duration: 0, Progress: 50 },
                { TaskID: 3, TaskName: 'Perform Soil test', StartDate: new Date('04/02/2019'), Duration: 4, Progress: 50  },
                { TaskID: 4, TaskName: 'Soil test approval', StartDate: new Date('04/02/2019'), Duration: 4,Predecessor:"2FS", Progress: 50 },
            ]
        },
        {
            TaskID: 5,
            TaskName: 'Project Estimation',
            StartDate: new Date('04/02/2019'),
            EndDate: new Date('04/21/2019'),
            subtasks: [
                { TaskID: 6, TaskName: 'Develop floor plan for estimation', StartDate: new Date('04/04/2019'), Duration: 3, Progress: 50 },
                { TaskID: 7, TaskName: 'List materials', StartDate: new Date('04/04/2019'), Duration: 3, Progress: 50 },
                { TaskID: 8, TaskName: 'Estimation approval', StartDate: new Date('04/04/2019'), Duration: 0,Predecessor:"6SS", Progress: 50 }
            ]
        },
    ];
	
var ganttChart = new ej.gantt.Gantt({
         dataSource: GanttData,
		 height:'450px',
		 taskFields: {
            id: 'TaskID',
            name: 'TaskName',
		    startDate: 'StartDate',
			dependency:'Predecessor',
            duration: 'Duration',
            progress: 'Progress',
			child: 'subtasks',
        }
	 });
ganttChart.appendTo('#Gantt');
<!DOCTYPE html><html lang="en"><head>
    <title>EJ2 Gantt</title>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta name="description" content="Typescript Gantt Controls">
    <meta name="author" content="Syncfusion">
    <link href="index.css" rel="stylesheet">
	<link href="https://cdn.syncfusion.com/ej2/material.css" rel="stylesheet" type="text/css">
    
    
<script src="https://cdn.syncfusion.com/ej2/26.1.35/dist/ej2.min.js" type="text/javascript"></script>
<script src="es5-datasource.js" type="text/javascript"></script>
<script src="https://cdn.syncfusion.com/ej2/syncfusion-helper.js" type ="text/javascript"></script>
</head>

<body>
       
    
    <div id="container">
        <div id="Gantt"></div>        
    </div>


<script>
var ele = document.getElementById('container');
if(ele) {
  ele.style.visibility = "visible";
}   
      </script>
<script src="index.js" type="text/javascript"></script>
</body></html>

Predecessor offset with duration units

In the Gantt control, the predecessor offset can be defined with the following duration units:

  • Day
  • Hour
  • Minute

You can define an offset with various offset duration units for predecessors by using the following code example.

var ganttData = [
        {
            TaskID: 1,
            TaskName: 'Project Initiation',
            StartDate: new Date('04/02/2019'),
            EndDate: new Date('04/21/2019'),
            subtasks: [
                { TaskID: 2, TaskName: 'Identify Site location', StartDate: new Date('04/02/2019'), Duration: 0, Progress: 50 },
                { TaskID: 3, TaskName: 'Perform Soil test', StartDate: new Date('04/02/2019'), Duration: 4, Progress: 50  },
                { TaskID: 4, TaskName: 'Soil test approval', StartDate: new Date('04/04/2019'), Duration: 4,Predecessor:"2FS+2days", Progress: 50 },
				{ TaskID: 5, TaskName: 'Clear the building site', StartDate: new Date('04/04/2019'), Duration: 2, Progress: 30, Predecessor: '4FF+960m'}
            ]
        },
        {
            TaskID: 6,
            TaskName: 'Project Estimation',
            StartDate: new Date('04/02/2019'),
            EndDate: new Date('04/21/2019'),
            subtasks: [
                { TaskID: 7, TaskName: 'Develop floor plan for estimation', StartDate: new Date('04/04/2019'), Duration: 3, Progress: 50 },
                { TaskID: 8, TaskName: 'List materials', StartDate: new Date('04/04/2019'), Duration: 3, Progress: 50 },
                { TaskID: 9, TaskName: 'Estimation approval', StartDate: new Date('04/06/2019'), Duration: 0,Predecessor:"7SS+16h", Progress: 50 }
            ]
        },
    ];
	
var ganttChart = new ej.gantt.Gantt({
         dataSource: ganttData,
		 height:'450px',
		 taskFields: {
            id: 'TaskID',
            name: 'TaskName',
		    startDate: 'StartDate',
			dependency:'Predecessor',
            duration: 'Duration',
            progress: 'Progress',
			child: 'subtasks',
        },
	    columns: [
            { field: 'TaskID', headerText: 'Task ID', textAlign: 'Left', width: '100' },
		    { field: 'Predecessor', headerText: 'Depedency', width: '150'},
            { field: 'TaskName', headerText: 'Task Name', width: '150' },
			{ field: 'StartDate', headerText: 'Start Date', width: '150' },
            { field: 'Duration', headerText: 'Duration', width: '150' },
            { field: 'Progress', headerText: 'Progress', width: '150'}
        ]
});
ganttChart.appendTo('#Gantt');
<!DOCTYPE html><html lang="en"><head>
    <title>EJ2 Gantt</title>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta name="description" content="Typescript Gantt Controls">
    <meta name="author" content="Syncfusion">
    <link href="index.css" rel="stylesheet">
	<link href="https://cdn.syncfusion.com/ej2/material.css" rel="stylesheet" type="text/css">
    
    
<script src="https://cdn.syncfusion.com/ej2/26.1.35/dist/ej2.min.js" type="text/javascript"></script>
<script src="es5-datasource.js" type="text/javascript"></script>
<script src="https://cdn.syncfusion.com/ej2/syncfusion-helper.js" type ="text/javascript"></script>
</head>

<body>
       
    
    <div id="container">
        <div id="Gantt"></div>        
    </div>


<script>
var ele = document.getElementById('container');
if(ele) {
  ele.style.visibility = "visible";
}   
      </script>
<script src="index.js" type="text/javascript"></script>
</body></html>

Disabling automatic dependency offset updates

By default, the dependency offsets are automatically updated in the Gantt chart whenever a task’s start or end date is changed. However, if you want to disable this feature, you can do so by disabling the updateOffsetOnTaskbarEdit property. Once this property is disabled, you can only update the offset value by editing the predecessor column cell or the offset column in the dependency tab of the edit dialog.

var ganttData = [
        {
            TaskID: 1,
            TaskName: 'Project Initiation',
            StartDate: new Date('04/02/2019'),
            EndDate: new Date('04/21/2019'),
            subtasks: [
                { TaskID: 2, TaskName: 'Identify Site location', StartDate: new Date('04/02/2019'), Duration: 0, Progress: 50 },
                { TaskID: 3, TaskName: 'Perform Soil test', StartDate: new Date('04/02/2019'), Duration: 4, Progress: 50  },
                { TaskID: 4, TaskName: 'Soil test approval', StartDate: new Date('04/04/2019'), Duration: 4,Predecessor:"2FS+2days", Progress: 50 },
				{ TaskID: 5, TaskName: 'Clear the building site', StartDate: new Date('04/04/2019'), Duration: 2, Progress: 30, Predecessor: '4FF+960m'}
            ]
        },
        {
            TaskID: 6,
            TaskName: 'Project Estimation',
            StartDate: new Date('04/02/2019'),
            EndDate: new Date('04/21/2019'),
            subtasks: [
                { TaskID: 7, TaskName: 'Develop floor plan for estimation', StartDate: new Date('04/04/2019'), Duration: 3, Progress: 50 },
                { TaskID: 8, TaskName: 'List materials', StartDate: new Date('04/04/2019'), Duration: 3, Progress: 50 },
                { TaskID: 9, TaskName: 'Estimation approval', StartDate: new Date('04/06/2019'), Duration: 0,Predecessor:"7SS+16h", Progress: 50 }
            ]
        },
    ];
	
var ganttChart = new ej.gantt.Gantt({
         dataSource: ganttData,
		 height:'450px',
		 taskFields: {
            id: 'TaskID',
            name: 'TaskName',
		    startDate: 'StartDate',
			dependency:'Predecessor',
            duration: 'Duration',
            progress: 'Progress',
			child: 'subtasks',
        },
	    columns: [
            { field: 'TaskID', headerText: 'Task ID', textAlign: 'Left', width: '100' },
		    { field: 'Predecessor', headerText: 'Depedency', width: '150'},
            { field: 'TaskName', headerText: 'Task Name', width: '150' },
			{ field: 'StartDate', headerText: 'Start Date', width: '150' },
            { field: 'Duration', headerText: 'Duration', width: '150' },
            { field: 'Progress', headerText: 'Progress', width: '150'}
        ]
});
ganttChart.appendTo('#Gantt');
<!DOCTYPE html><html lang="en"><head>
    <title>EJ2 Gantt</title>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta name="description" content="Typescript Gantt Controls">
    <meta name="author" content="Syncfusion">
    <link href="index.css" rel="stylesheet">
	<link href="https://cdn.syncfusion.com/ej2/material.css" rel="stylesheet" type="text/css">
    
    
<script src="https://cdn.syncfusion.com/ej2/26.1.35/dist/ej2.min.js" type="text/javascript"></script>
<script src="es5-datasource.js" type="text/javascript"></script>
<script src="https://cdn.syncfusion.com/ej2/syncfusion-helper.js" type ="text/javascript"></script>
</head>

<body>
       
    
    <div id="container">
        <div id="Gantt"></div>        
    </div>


<script>
var ele = document.getElementById('container');
if(ele) {
  ele.style.visibility = "visible";
}   
      </script>
<script src="index.js" type="text/javascript"></script>
</body></html>

In Gantt, task relationship link can be broken by editing the start date, end date and duration value of task. When the task relationship broken on any edit action. This can be handled in Gantt in two ways.

  • Using actionBegin event
  • Using predecessor validation dialog

Using actionBegin event

When the task relationship link is broken on any edit action, then the actionBegin event will be triggered with requestType argument as validateLinkedTask. You can validate the editing action within the actionBegin event using the validateMode event argument. The validateMode event argument has the following properties:

Argument Default value Description
args.validateMode.respectLink false In this validation mode, the predecessor links get high priority. With this mode enabled, when the successor task is moved before the predecessor task’s end date, the editing will be reverted, and dates will be validated based on the dependency links.
args.validateMode.removeLink false In this validation mode, the taskbar editing gets high priority. For inappropriate task dates, the dependency links will be removed and tasks will be moved to the edited date.
args.validateMode.preserveLinkWithEditing true In this validation mode, the taskbar editing will be considered along with the dependency links. This relationship will be maintained by updating the offset value of predecessors.

By default, the preserveLinkWithEditing validation mode will be enabled, so the predecessors are updated with offset values.

The following sample explains enabling the respectLink validation mode while editing the linked tasks in the actionBegin event.

var GanttData = [
        {
            TaskID: 1,
            TaskName: 'Project Initiation',
            StartDate: new Date('04/02/2019'),
            EndDate: new Date('04/21/2019'),
            subtasks: [
                { TaskID: 2, TaskName: 'Identify Site location', StartDate: new Date('04/02/2019'), Duration: 0, Progress: 50 },
                { TaskID: 3, TaskName: 'Perform Soil test', StartDate: new Date('04/02/2019'), Duration: 4, Progress: 50  },
                { TaskID: 4, TaskName: 'Soil test approval', StartDate: new Date('04/02/2019'), Duration: 4,Predecessor:"2FS", Progress: 50 },
            ]
        },
        {
            TaskID: 5,
            TaskName: 'Project Estimation',
            StartDate: new Date('04/02/2019'),
            EndDate: new Date('04/21/2019'),
            subtasks: [
                { TaskID: 6, TaskName: 'Develop floor plan for estimation', StartDate: new Date('04/04/2019'), Duration: 3, Progress: 50 },
                { TaskID: 7, TaskName: 'List materials', StartDate: new Date('04/04/2019'), Duration: 3, Progress: 50 },
                { TaskID: 8, TaskName: 'Estimation approval', StartDate: new Date('04/04/2019'), Duration: 0,Predecessor:"6SS", Progress: 50 }
            ]
        },
    ];

	
var ganttChart = new ej.gantt.Gantt({
         dataSource: GanttData,
		 height:'450px',
		 taskFields: {
            id: 'TaskID',
            name: 'TaskName',
		    startDate: 'StartDate',
			dependency:'Predecessor',
            duration: 'Duration',
            progress: 'Progress',
			child: 'subtasks',
        },
		editSettings:{
			allowTaskbarEditing:true
		},
		actionBegin:function(args){
	       if (args.requestType == "validateLinkedTask") {
              args.validateMode.respectLink = true;
            }
		}
});
ganttChart.appendTo('#Gantt');
<!DOCTYPE html><html lang="en"><head>
    <title>EJ2 Gantt</title>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta name="description" content="Typescript Gantt Controls">
    <meta name="author" content="Syncfusion">
    <link href="index.css" rel="stylesheet">
	<link href="https://cdn.syncfusion.com/ej2/material.css" rel="stylesheet" type="text/css">
    
    
<script src="https://cdn.syncfusion.com/ej2/26.1.35/dist/ej2.min.js" type="text/javascript"></script>
<script src="es5-datasource.js" type="text/javascript"></script>
<script src="https://cdn.syncfusion.com/ej2/syncfusion-helper.js" type ="text/javascript"></script>
</head>

<body>
       
    
    <div id="container">
        <div id="Gantt"></div>        
    </div>


<script>
var ele = document.getElementById('container');
if(ele) {
  ele.style.visibility = "visible";
}   
      </script>
<script src="index.js" type="text/javascript"></script>
</body></html>

Using validation dialog

When disabling all the validation modes in the actionBegin event, a validation pop-up will be displayed prompting users to select the validation mode to validate taskbar editing.

This validation pop-up will display different options based on the successor task’s start date after editing.

If you move the successor task that starts after the predecessor task’s end date, then a dialog will be rendered with the following options:

  • Cancel, Keep the existing link.
  • Remove the link and move the task to start on edited date.
  • Move the task to start on edited date and keep the link.

If you move the successor task that starts before the predecessor task’s end date, then a dialog will be rendered with the following options:

  • Cancel, Keep the existing link.
  • Remove the link and move the task to start on edited date.

The following code example shows how to enable the predecessor validation dialog in Gantt.

var GanttData = [
        {
            TaskID: 1,
            TaskName: 'Project Initiation',
            StartDate: new Date('04/02/2019'),
            EndDate: new Date('04/21/2019'),
            subtasks: [
                { TaskID: 2, TaskName: 'Identify Site location', StartDate: new Date('04/02/2019'), Duration: 0, Progress: 50 },
                { TaskID: 3, TaskName: 'Perform Soil test', StartDate: new Date('04/02/2019'), Duration: 4, Progress: 50  },
                { TaskID: 4, TaskName: 'Soil test approval', StartDate: new Date('04/02/2019'), Duration: 4,Predecessor:"2FS", Progress: 50 },
            ]
        },
        {
            TaskID: 5,
            TaskName: 'Project Estimation',
            StartDate: new Date('04/02/2019'),
            EndDate: new Date('04/21/2019'),
            subtasks: [
                { TaskID: 6, TaskName: 'Develop floor plan for estimation', StartDate: new Date('04/04/2019'), Duration: 3, Progress: 50 },
                { TaskID: 7, TaskName: 'List materials', StartDate: new Date('04/04/2019'), Duration: 3, Progress: 50 },
                { TaskID: 8, TaskName: 'Estimation approval', StartDate: new Date('04/04/2019'), Duration: 0,Predecessor:"6SS", Progress: 50 }
            ]
        },
    ];
	
var ganttChart = new ej.gantt.Gantt({
         dataSource: GanttData,
		 height:'450px',
		 taskFields: {
            id: 'TaskID',
            name: 'TaskName',
		    startDate: 'StartDate',
			dependency:'Predecessor',
            duration: 'Duration',
            progress: 'Progress',
			child: 'subtasks'
        },
		editSettings:{
			allowTaskbarEditing:true
		},
		actionBegin:function(args){
	       if (args.requestType == "validateLinkedTask") {
              args.validateMode.preserveLinkWithEditing = false;
            }
		}
});
ganttChart.appendTo('#Gantt');
<!DOCTYPE html><html lang="en"><head>
    <title>EJ2 Gantt</title>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta name="description" content="Typescript Gantt Controls">
    <meta name="author" content="Syncfusion">
    <link href="index.css" rel="stylesheet">
	<link href="https://cdn.syncfusion.com/ej2/material.css" rel="stylesheet" type="text/css">
    
    
<script src="https://cdn.syncfusion.com/ej2/26.1.35/dist/ej2.min.js" type="text/javascript"></script>
<script src="es5-datasource.js" type="text/javascript"></script>
<script src="https://cdn.syncfusion.com/ej2/syncfusion-helper.js" type ="text/javascript"></script>
</head>

<body>
       
    
    <div id="container">
        <div id="Gantt"></div>        
    </div>


<script>
var ele = document.getElementById('container');
if(ele) {
  ele.style.visibility = "visible";
}   
      </script>
<script src="index.js" type="text/javascript"></script>
</body></html>

Dynamically show/hide the dependency line

By default, mapping the dependency field in taskFields displays dependency lines in the Gantt chart. To hide the dependency line upon button click, set visibility style to hidden for the CSS class name .e-gantt-dependency-view-container.

var ganttData = [
    {
      TaskID: 1,
      TaskName: 'Project Initiation',
      StartDate: new Date('04/02/2019'),
      EndDate: new Date('04/21/2019'),
      subtasks: [
        { TaskID: 2, TaskName: 'Identify Site location', StartDate: new Date('04/02/2019'), Duration: 0, Progress: 50, },
        { TaskID: 3, TaskName: 'Perform Soil test', StartDate: new Date('04/02/2019'), Duration: 4, Progress: 50, },
        { TaskID: 4, TaskName: 'Soil test approval', StartDate: new Date('04/04/2019'), Duration: 4, Predecessor: '2FS+2days', Progress: 50, },
        { TaskID: 5, TaskName: 'Clear the building site', StartDate: new Date('04/04/2019'), Duration: 2, Progress: 30, Predecessor: '4FF+960m', },
      ],
    },
    {
      TaskID: 6,
      TaskName: 'Project Estimation',
      StartDate: new Date('04/02/2019'),
      EndDate: new Date('04/21/2019'),
      subtasks: [
        { TaskID: 7, TaskName: 'Develop floor plan for estimation', StartDate: new Date('04/04/2019'), Duration: 3, Progress: 50, },
        { TaskID: 8, TaskName: 'List materials', StartDate: new Date('04/04/2019'), Duration: 3, Progress: 50, },
        { TaskID: 9, TaskName: 'Estimation approval', StartDate: new Date('04/06/2019'), Duration: 0, Predecessor: '7SS+16h', Progress: 50, },
      ],
    },
  ];
  
  // Switch toggle.
  var switchObj = new ej.buttons.Switch({ checked: false, change: Onchange, });
  switchObj.appendTo('#switch');
  function Onchange() {
    var ganttDependencyViewContainer = document.querySelector('.e-gantt-dependency-view-container');
    if (switchObj.checked) {
		ganttDependencyViewContainer.style.visibility = 'hidden';
    }
    else {
        ganttDependencyViewContainer.style.visibility = 'visible';
    }
  }
  var ganttChart = new ej.gantt.Gantt({
    dataSource: ganttData,
    height: '450px',
    taskFields: {
      id: 'TaskID',
      name: 'TaskName',
      startDate: 'StartDate',
      dependency: 'Predecessor',
      duration: 'Duration',
      progress: 'Progress',
      child: 'subtasks',
    },
    columns: [
      { field: 'TaskID', headerText: 'Task ID', textAlign: 'Left', width: '100' },
      { field: 'Predecessor', headerText: 'Depedency', width: '150' },
      { field: 'TaskName', headerText: 'Task Name', width: '150' },
      { field: 'StartDate', headerText: 'Start Date', width: '150' },
      { field: 'Duration', headerText: 'Duration', width: '150' },
      { field: 'Progress', headerText: 'Progress', width: '150' },
    ],
  });
  ganttChart.appendTo('#Default');
<html>
  <head>
    <script src="https://ej2.syncfusion.com/javascript/demos/gantt/default/datasource.js" type="text/javascript"></script>
    <script src="https://cdn.syncfusion.com/ej2/26.1.35/dist/ej2.min.js" type="text/javascript"></script>
    <link href="https://cdn.syncfusion.com/ej2/26.1.35/material.css" rel="stylesheet"/>
    <link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet"/>
    <style> body { touch-action: none; } </style>
  <script src="https://cdn.syncfusion.com/ej2/syncfusion-helper.js" type ="text/javascript"></script>
</head>
  <body>
    <div class="stackblitz-container material3">
      <div class="control-section">
        <div class="content-wrapper">
          <label>Show/Hide Dependency Line</label>
          <input type="checkbox" id="switch" />
          <div id="Default"></div>
        </div>
      </div>
    </div>
    <script src="index.js" type="text/javascript"></script>
  </body>
</html>