Worker: Worker() constructor

The Worker() constructor creates a Worker object that executes the script at the specified URL. This script must obey the same-origin policy.

Note: that there is a disagreement among browser manufacturers about whether a data URL is of the same origin or not. Though Firefox 10 and later accept data URLs, that's not the case in all other browsers.


new Worker(aURL)
new Worker(aURL, options)



A string representing the URL of the script the worker will execute. It must obey the same-origin policy.

options Optional

An object containing option properties that can be set when creating the object instance. Available properties are as follows:


A string specifying the type of worker to create. The value can be classic or module. If not specified, the default used is classic.


A string specifying the type of credentials to use for the worker. The value can be omit, same-origin, or include. If not specified, or if type is classic, the default used is omit (no credentials required).


A string specifying an identifying name for the DedicatedWorkerGlobalScope representing the scope of the worker, which is mainly useful for debugging purposes.


SecurityError DOMException

Thrown if the document is not allowed to start workers, e.g. if the URL has an invalid syntax or if the same-origin policy is violated.

NetworkError DOMException

Thrown if the MIME type of the worker script is incorrect. It should always be text/javascript (for historical reasons other JavaScript MIME types may be accepted).

SyntaxError DOMException

Thrown if aURL cannot be parsed.


The following code snippet shows creation of a Worker object using the Worker() constructor and subsequent usage of the object:

const myWorker = new Worker("worker.js");
const first = document.querySelector("input#number1");

first.onchange = () => {
  console.log("Message posted to worker");

For a full example, see our Basic dedicated worker example (run dedicated worker).


HTML Standard
# dom-worker-dev

Browser compatibility

BCD tables only load in the browser

See also

The Worker interface it belongs to.