Critical Path

The critical path is the chain of tasks with zero slack — delay any of them and the whole project finishes later. FluxGantt computes it with the classic CPM (Critical Path Method): topological sort → forward pass (early start/finish) → backward pass (late start/finish) → slack. It honors dependency type, lag/lead, and the working calendar.

Computing it

const result = gantt.computeCriticalPath(); // CriticalPathResult

computeCriticalPath() throws if there are no tasks, and propagates a CyclicDependencyError if the graph somehow contains a cycle (normal linkTasks usage can't create one — see Dependencies). Calling it also emits critical-path:computed with the critical task ids.

CriticalPathResult

interface CriticalPathResult {
  readonly schedule: ReadonlyMap<TaskId, TaskSchedule>;
  readonly criticalTaskIds: readonly TaskId[]; // in input-task order
  readonly projectEnd: Temporal.ZonedDateTime;
}

Each TaskSchedule carries the computed timing for one task:

interface TaskSchedule {
  readonly taskId: TaskId;
  readonly earlyStart: Temporal.ZonedDateTime;
  readonly earlyFinish: Temporal.ZonedDateTime;
  readonly lateStart: Temporal.ZonedDateTime;
  readonly lateFinish: Temporal.ZonedDateTime;
  readonly slackHours: number;   // working hours, ≥ 0
  readonly isCritical: boolean;  // true when slack ≈ 0
}

Example:

const { criticalTaskIds, projectEnd, schedule } = gantt.computeCriticalPath();
 
console.log('project ends:', projectEnd.toString());
for (const id of criticalTaskIds) {
  console.log('critical:', gantt.getTask(id)?.name);
}
console.log('slack on build:', schedule.get(toTaskId('build'))?.slackHours);

The critical-path:computed event

When mounted, FluxGantt recomputes the critical path reactively as tasks/dependencies change, and emits critical-path:computed only when the critical set actually changes — not on every mutation:

gantt.on('critical-path:computed', (criticalTaskIds) => {
  console.log('critical tasks:', criticalTaskIds.length);
});

Distinguishable without color

Critical bars are rendered with a dashed outline in addition to the critical-path red (--fg-task-critical, #ef4444) — not color alone. That means the critical path stays distinguishable under color-blindness and in grayscale print, satisfying WCAG's "don't rely on color" guidance. You can tune the dash via the --fg-task-critical-dash custom property; see Theming.