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

It is implemented by both Window and WorkerGlobalScope. The existence of the property indicates that the API is supported in the current context, and can be accessed using this.scheduler.

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

A Scheduler.

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 this) {
  // 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.
  scheduler
    .postTask(myTask)
    // 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 API
• Scheduler.postTask()
• TaskController