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TaskPriorityChangeEvent: previousPriority property

The readonly previousPriority property of the TaskPriorityChangeEvent interface returns the priority of the corresponding 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.

The new priority of the task can be read from event.target.priority.

Value

A string, indicating the associated task's priority before it was changed. This will be one of: "user-blocking", "user-visible", "background".

Examples

The code below shows the previousPriority being obtained in a handler for a prioritychange event.

js

// 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

Browser compatibility

Desktop Mobile
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet
previousPriority 94 94 101 No 80 No 94 94 No 66 No 17.0

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https://developer.mozilla.org/en-US/docs/Web/API/TaskPriorityChangeEvent/previousPriority