files/en-us/web/api/taskprioritychangeevent/previouspriority/index.md
{{APIRef("Prioritized Task Scheduling API")}}{{AvailableInWorkers}}
The previousPriority read-only property of the {{domxref("TaskPriorityChangeEvent")}} interface returns the priority of the corresponding {{domxref("TaskSignal")}} before it was changed and this prioritychange event was emitted.
This is the value that was set in the TaskPriorityChangeEvent constructor argument options.previous. <!-- link? -->
The new priority of the task can be read from event.target.priority.
A string, indicating the associated task's priority before it was changed.
This will be one of: "user-blocking", "user-visible", "background".
The code below shows the previousPriority being obtained in a handler for a prioritychange event.
// Listen for 'prioritychange' events on the controller's signal.
controller.signal.addEventListener("prioritychange", (event) => {
const previousPriority = event.previousPriority;
const newPriority = event.target.priority;
console.log(
`The priority changed from ${previousPriority} to ${newPriority}.`,
);
});
A more complete live example can be found in prioritychange event > Examples.
{{Specifications}}
{{Compat}}