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Prioritized Task Scheduler Demo - Online scheduler.postTask()

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Your browser doesn't support scheduler.postTask(). This demo will use a fallback (setTimeout) and priorities will not be honored.

Prioritized Task Scheduler Demo

Visualize how the scheduler.postTask() API schedules tasks with different priorities (user-blocking, user-visible, background). Add tasks, set delays, cancel them, and watch the execution order in real time.

Add New Task

“Run” will schedule all pending tasks using scheduler.postTask().

Task Queue
0
Name Priority Delay Status Action
No tasks added yet. Add some above!
Execution Log
Waiting for tasks to execute...

Frequently Asked Questions

scheduler.postTask() is a modern browser API that allows developers to schedule tasks with a specified priority. It helps the browser decide which tasks to run first, improving responsiveness by prioritizing user-facing work over background operations.

Three priority levels are defined: user-blocking (for tasks that block user interaction, like rendering), user-visible (for tasks visible to the user but not critical, like loading secondary content), and background (for tasks that can run in idle time, like analytics).

setTimeout simply schedules a callback after a minimum delay without considering priority. scheduler.postTask() allows the browser to interleave tasks based on their importance, leading to smoother user experiences, especially under load.

Yes, by passing an AbortSignal (from an AbortController) to the options. When controller.abort() is called, the task is cancelled before it starts, and the promise rejects with an AbortError.

As of 2025, scheduler.postTask() is supported in Chromium-based browsers (Chrome, Edge, Opera). Firefox and Safari are still evaluating the specification. This demo includes a fallback for unsupported browsers.

Yes, the Scheduling API is available in both window and worker contexts, though the priority levels are the same. This makes it useful for offloading background logic while still respecting priority.
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