Window: scheduler property

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

The scheduler read-only property of the Window interface is the entry point for using the Prioritized Task Scheduling API.

The object has a single instance method Scheduler.postTask() that is used to post prioritized tasks for scheduling.



The code below shows a very basic use of the property and its associated interface. It demonstrates how to check that the property exists and then posts a task that returns a promise.

// Check if the prioritized task API is supported
if ("scheduler" in window) {
  // Callback function - "the task"
  const myTask = () => "Task 1: user-visible";

  // Post task with default priority: 'user-visible' (no other options)
  // When the task resolves, Promise.then() logs the result.
    // Handle resolved value
    .then((taskResult) => console.log(`${taskResult}`))
    // Handle error or abort
    .catch((error) => console.log(`Error: ${error}`));
} else {
  console.log("Feature: NOT Supported");

For comprehensive example code showing to use the API see Prioritized Task Scheduling API > Examples.


Prioritized Task Scheduling
# dom-windoworworkerglobalscope-scheduler

Browser compatibility

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See also