# Worker Startup >![](../../public_sys-resources/icon-note.gif) **NOTE:** >The initial APIs of this module are supported since API version 7. Newly added APIs will be marked with a superscript to indicate their earliest API version. ## Modules to Import ``` import worker from '@ohos.worker'; ``` ## Required Permissions None ## Attributes

Name	Type	Readable	Writable	Description
parentPort	DedicatedWorkerGlobalScope	Yes	Yes	Object of the worker thread used to communicate with the host thread.

## WorkerOptions Provides options that can be set for the worker to create.

Name	Type	Readable	Writable	Description
type	"classic"	Yes	Yes	Mode in which the worker executes the script.
name	string	Yes	Yes	Name of the worker.

## Worker Before using the following methods, you must construct a worker instance. The **worker** class inherits from [EventTarget](#section256019311465). ### constructor constructor\(scriptURL: string, options?: WorkerOptions\) A constructor used to create a worker instance. - Parameters

Name	Type	Mandatory	Description
scriptURL	string	Yes	URL of the script to be executed by the worker. The script is stored in the workers directory, which is in the same directory as the pages directory of the new DevEco Studio project. If the workers directory does not exist, you need to create it.
options	WorkerOptions	No	Options that can be set for the worker.

- Return values

Name	Description
worker	Returns the worker instance created; returns undefined if the worker instance fails to be created.

- Example ``` import worker from '@ohos.worker'; const worker = new worker.Worker("workers/worker.js", {name:"first worker"}); ``` ### postMessage postMessage\(message: Object, options?: PostMessageOptions\): void Sends a message to the worker thread. The data is transferred using the structured clone algorithm. - Parameters

Name	Type	Mandatory	Description
message	Object	Yes	Data to be sent to the worker.
options	PostMessageOptions	No	ArrayBuffer instances that can be transferred. The transferList array cannot contain null.

- Example ``` import worker from '@ohos.worker'; const worker = new worker.Worker("workers/worker.js"); worker.postMessage("hello world"); const worker = new worker.Worker("workers/worker.js"); var buffer = new ArrayBuffer(8); worker.postMessage(buffer, [buffer]); ``` ### on on\(type: string, listener: EventListener\): void Adds an event listener to the worker. - Parameters

Name	Type	Mandatory	Description
type	string	Yes	Type of the event to listen for.
listener	EventListener	Yes	Callback to invoke when an event of the specified type occurs.

- Example ``` import worker from '@ohos.worker'; const worker = new worker.Worker("workers/worker.js") worker.on("alert", (e)=>{ console.log("alert listener callback"); }) ``` ### once once\(type: string, listener: EventListener\): void Adds an event listener to the worker and removes the event listener automatically after it is invoked once. - Parameters

Name	Type	Mandatory	Description
type	string	Yes	Type of the event to listen for.
listener	EventListener	Yes	Callback to invoke when an event of the specified type occurs.

- Example ``` import worker from '@ohos.worker'; const worker = new worker.Worker("workers/worker.js"); worker.once("alert", (e)=>{ console.log("alert listener callback"); }) ``` ### off off\(type: string, listener?: EventListener\): void Removes an event listener for the worker. - Parameters

Name	Type	Mandatory	Description
type	string	Yes	Type of the event for which the event listener is removed.
listener	EventListener	No	Callback of the event listener to remove.

- Example ``` import worker from '@ohos.worker'; const worker = new worker.Worker("workers/worker.js"); worker.off("alert"); ``` ### terminate terminate\(\): void Terminates the worker thread to stop the worker from receiving messages. - Example ``` import worker from '@ohos.worker'; const worker = new worker.Worker("workers/worker.js") worker.terminate() ``` ### onexit onexit?: \(code: number\) =\> void Defines the event handler to be called when the worker exits. The handler is executed in the host thread. - Parameters

Name	Type	Mandatory	Description
code	number	No	Code indicating the worker exit state.

- Example ``` import worker from '@ohos.worker'; const worker = new worker.Worker("workers/worker.js") worker.onexit = function(e) { console.log("onexit") } ``` ### onerror onerror?: \(err: ErrorEvent\) =\> void Defines the event handler to be called when an exception occurs during worker execution. The event handler is executed in the host thread. - Parameters

Name	Type	Mandatory	Description
err	ErrorEvent	No	Error data.

- Example ``` import worker from '@ohos.worker'; const worker = new worker.Worker("workers/worker.js") worker.onerror = function(e) { console.log("onerror") } ``` ### onmessage onmessage?: \(event: MessageEvent\) =\> void Defines the event handler to be called when the host thread receives a message created by itself and sent by the worker through the **parentPort.postMessage**. The event handler is executed in the host thread. - Parameters

Name	Type	Mandatory	Description
event	MessageEvent	No	Message received.

- Example ``` import worker from '@ohos.worker'; const worker = new worker.Worker("workers/worker.js") worker.onmessage = function(e) { console.log("onerror") } ``` ### onmessageerror onmessageerror?: \(event: MessageEvent\) =\> void Defines the event handler to be called when the worker receives a message that cannot be serialized. The event handler is executed in the host thread. - Parameters

Name	Type	Mandatory	Description
event	MessageEvent	No	Error data.

- Example ``` import worker from '@ohos.worker'; const worker = new worker.Worker("workers/worker.js") worker.onmessageerror= function(e) { console.log("onmessageerror") } ``` ## EventTarget ### addEventListener addEventListener\(type: string, listener: EventListener\): void Adds an event listener to the worker. - Parameters

Name	Type	Mandatory	Description
type	string	Yes	Type of the event to listen for.
listener	EventListener	Yes	Callback to invoke when an event of the specified type occurs.

- Example ``` import worker from '@ohos.worker'; const worker = new worker.Worker("workers/worker.js") worker.addEventListener("alert", (e)=>{ console.log("alert listener callback"); }) ``` ### removeEventListener removeEventListener\(type: string, callback?: EventListener\): void Removes an event listener for the worker. - Parameters

Name	Type	Mandatory	Description
type	string	Yes	Type of the event for which the event listener is removed.
callback	EventListener	No	Callback of the event listener to remove.

- Example ``` import worker from '@ohos.worker'; const worker = new worker.Worker("workers/worker.js") worker.removeEventListener("alert") ``` ### dispatchEvent dispatchEvent\(event: Event\): boolean Dispatches the event defined for the worker. - Parameters

Name	Type	Mandatory	Description
event	Event	Yes	Event to dispatch.

- Return values

Name	Description
boolean	Returns true if the event is dispatched successfully; returns false otherwise.

- Example ``` import worker from '@ohos.worker'; const worker = new worker.Worker("workers/worker.js") worker.dispatchEvent({type:"alert"}) ``` ### removeAllListener removeAllListener\(\): void Removes all event listeners for the worker. - Example ``` import worker from '@ohos.worker'; const worker = new worker.Worker("workers/worker.js") worker.removeAllListener({type:"alert"}) ``` ## DedicatedWorkerGlobalScope Implements communication between the worker thread and the host thread. The **postMessage** API is used to send messages to the host thread, and the **close** API is used to terminate the worker thread. The **DedicatedWorkerGlobalScope** class inherits from [WorkerGlobalScope](#section12882825611). ### postMessage postMessage\(message: Object, options?: PostMessageOptions\): void Sends a message to the host thread from the worker. - Parameters

Name	Type	Mandatory	Description
message	Object	Yes	Data to be sent to the worker.
options	PostMessageOptions	No	ArrayBuffer instances that can be transferred. The transferList array cannot contain null.

- Example ``` // main.js import worker from '@ohos.worker'; const worker = new worker.Worker("workers/worker.js") worker.postMessage("hello world") worker.onmessage = function(e) { console.log("receive data from worker.js") } // worker.js import worker from "@ohos.worker"; const parentPort = worker.parentPort; parentPort.onmessage = function(e){ parentPort.postMessage("receive data from main.js") } ``` ### close close\(\): void Closes the worker thread to stop the worker from receiving messages. - Example ``` // main.js import worker from '@ohos.worker'; const worker = new worker.Worker("workers/worker.js") // worker.js import worker from "@ohos.worker"; const parentPort = worker.parentPort; parentPort.onmessage = function(e) { parentPort.close() } ``` ### onmessage onmessage?: \(event: MessageEvent\) =\> void Defines the event handler to be called when the worker thread receives a message sent by the host thread through **worker.postMessage**. The event handler is executed in the worker thread. - Parameters

Name	Type	Mandatory	Description
event	MessageEvent	No	Message received.

- Example ``` // main.js import worker from '@ohos.worker'; const worker = new worker.Worker("workers/worker.js") worker.postMessage("hello world") // worker.js import worker from "@ohos.worker"; const parentPort = worker.parentPort; parentPort.onmessage = function(e) { console.log("receive main.js message") } ``` ### onmessageerror onmessageerror?: \(event: MessageEvent\) =\> void Defines the event handler to be called when the worker receives a message that cannot be deserialized. The event handler is executed in the worker thread. - Parameters

Name	Type	Mandatory	Description
event	MessageEvent	No	Error data.

- Example ``` // main.js import worker from '@ohos.worker'; const worker = new worker.Worker("workers/worker.js") // worker.js import worker from "@ohos.worker"; const parentPort = worker.parentPort; parentPort.onmessageerror= function(e) { console.log("worker.js onmessageerror") } ``` ## PostMessageOptions Specifies the object whose ownership needs to be transferred during data transfer. The object must be **ArrayBuffer**.

Name	Type	Readable	Writable	Description
transfer	Object[]	Yes	Yes	ArrayBuffer array used to transfer the ownership.

## Event Defines the event.

Name	Type	Readable	Writable	Description
type	string	Yes	No	Type of the event.
timeStamp	number	Yes	No	Timestamp (accurate to millisecond) when the event is created.

## EventListener Implements event listening. ### \(evt: Event\): void | Promise Specifies the callback to invoke. - Parameters

Name	Type	Mandatory	Description
evt	Event	Yes	Event class for the callback to invoke.

- Return values

Name	Description
void \| Promise<void>	Returns no value or returns a Promise.

- Example ``` import worker from '@ohos.worker'; const worker = new worker.Worker("workers/worker.js"); worker.addEventListener("alert", (e)=>{ console.log("alert listener callback"); }) ``` ## ErrorEvent Provides detailed information about the exception occurred during worker execution. The **ErrorEvent** class inherits from [Event](#section1674694018507).

Name	Type	Readable	Writable	Description
message	string	Yes	No	Information about the exception.
filename	string	Yes	No	File where the exception is located.
lineno	number	Yes	No	Number of the line where the exception is located.
colno	number	Yes	No	Number of the column where the exception is located.
error	Object	Yes	No	Type of the exception.

## MessageEvent Holds the data transferred between worker threads.

Name	Type	Readable	Writable	Description
data	T	Yes	No	Data transferred between threads.

## WorkerGlobalScope Defines the running environment of the worker thread. The **WorkerGlobalScope** class inherits from [EventTarget](#section256019311465). ### Attributes

Name	Type	Readable	Writable	Description
name	string	Yes	No	Worker name specified when there is a new worker.
self	WorkerGlobalScope & typeof globalThis	Yes	No	WorkerGlobalScope.

### onerror onerror?: \(ev: ErrorEvent\) =\> void Defines the event handler to be called when an exception occurs during worker execution. The event handler is executed in the worker thread. - Parameters

Name	Type	Mandatory	Description
ev	ErrorEvent	No	Error data.