DHTMLX Planning Engine Documentation

TaskData#

One task, summary or milestone as a plain object. Put tasks in ProjectData.tasks to load a plan, or in SchedulingChanges.tasks.add to add them to a live project. No call returns TaskData: scheduled dates come back as update entries in ScheduleResult.

Fields#

Field Type Default Description
id Id required Task id, unique among the project's tasks.
parent Id | null no parent Id of the parent task. "" or a value equal to SchedulingConfig.root_id also means a top-level task.
type "task" | "summary" | "project" | "milestone" "task" Plain task, summary or milestone. "project" is an alias of "summary". Decides which date fields are needed, see Dates by task type.
start_date DateValue | null none Start of the task.
end_date DateValue | null none End of the task. Must not be before start_date.
duration number | null none Working time in duration_unit. Finite and >= 0.
duration_unit TimeUnit | null config.duration_unit Unit of duration, leveling_delay and pauses.
constraint_type ConstraintType | null none Date constraint: "asap", "alap", "snet", "snlt", "fnet", "fnlt", "mso" or "mfo". Takes effect only when config.apply_constraints is true.
constraint_date DateValue | null none Date of the constraint. Required for every constraint_type except "asap" and "alap".
auto_scheduling boolean | null true false fixes the task: the scheduler never moves it.
unscheduled boolean | null false true leaves the task and all its descendants out of scheduling and out of results. Such tasks need no dates.
progress number | null 0 Completed share, from 0 to 1. With config.use_progress, 1 marks the task completed and fixed.
priority number | null 500 Leveling priority, an integer from 0 to 1000. Read only by Project#level.
leveling_delay number | null 0 Elapsed time added before the task's driven start, in duration_unit (a day is 24 hours). Finite and >= 0. Written by Project#level.
pauses Pause[] | null [] Splits in the task's work, sorted by at and non-overlapping. Written by Project#level. Ignored on summaries, milestones and unscheduled tasks.
calendar_id Id | null none Id of the task's working calendar: an entry of ProjectData.calendars, or "global". Without it the task uses the "global" calendar, or its nearest ancestor's calendar when config.calendar_mode is "task-inherited".

null on any optional field reads the same as leaving the field out. Unknown fields are ignored, so task objects from a Gantt UI can be passed as they are. Date fields take a string or a local Date; see DateValue.

Dates by task type#

start_date, end_date and duration are read differently for each type. Unscheduled tasks skip these rules.

type Accepted input Result
"task" start_date + duration End computed forward on the task's calendar, around any pauses.
"task" end_date + duration Start computed backward from the end.
"task" start_date + end_date duration is the working time between the dates.
"task" all three Accepted only when start_date + duration lands on end_date.
"summary" start_date + end_date The given span. duration is ignored.
"summary" neither date Span taken from the dated children.
"milestone" start_date or end_date A zero-length task at that date. duration is ignored.

A summary with only one of the two dates is an error, and so is a plain task with fewer than two of the three fields.

Errors#

With the default validation: "strict" (see Project), an invalid task makes Project#solve, Project#analyze and schedule throw an InputError with kind: "validation" at a path under tasks[i]:

path When it occurs
tasks[i].progress progress isn't finite or is outside 0..1
tasks[i].leveling_delay leveling_delay isn't finite or is negative
tasks[i].duration duration isn't finite or is negative; or all three date fields are set and disagree
tasks[i].constraint_date a dated constraint_type has no constraint_date
tasks[i].pauses[j] pause j has a negative or non-finite at, a non-finite or non-positive length, or is out of order or overlaps the previous one
tasks[i].calendar_id calendar_id names no calendar in ProjectData.calendars and isn't "global"
tasks[i].start_date a plain task has fewer than two of start_date, end_date, duration; a summary has only one date; a milestone has no date
tasks[i].end_date end_date is before start_date
tasks[i] a summary has no dates and no dated children

A priority that isn't a whole number from 0 to 1000 throws an InputError with kind: "validation" and path: null. Rules across tasks (unique ids, known parent, no hierarchy cycle) are on ProjectData. validation: "repair" fixes several of these cases instead of throwing.

Used by#

Example#

A summary with two dated children, a constrained task and a milestone:

const tasks = [
  { id: "phase", type: "summary" },
  { id: "design", parent: "phase", start_date: "2026-04-06 08:00", duration: 2 },
  {
    id: "build",
    parent: "phase",
    start_date: "2026-04-06 08:00",
    duration: 3,
    constraint_type: "snet",
    constraint_date: "2026-04-10 08:00",
  },
  { id: "release", type: "milestone", start_date: "2026-04-10 08:00" },
];