xref: /docs/en/application-dev/reference/apis-ability-kit/js-apis-app-ability-childProcessArgs.md

# @ohos.app.ability.ChildProcessArgs

The ChildProcessArgs module describes the parameters transferred to the child process. When starting a child process through [childProcessManager](js-apis-app-ability-childProcessManager.md), you can transfer parameters to the child process through **ChildProcessArgs**.

> **NOTE**
> 
> The initial APIs of this module are supported since API version 12. Newly added APIs will be marked with a superscript to indicate their earliest API version.
> 
> The APIs of this module can be used only in the stage model.

## Modules to Import

```ts
import { ChildProcessArgs } from '@kit.AbilityKit';
```

## Properties

**System capability**: SystemCapability.Ability.AbilityRuntime.Core

| Name       | Type                   | Mandatory| Description                                                        |
| ----------- | --------------------   | ---- | ------------------------------------------------------------ |
| entryParams | string                 |  No | Custom parameters to be transparently transmit to the child process. The parameters can be obtained through **args.entryParams** in [ChildProcess.onStart](js-apis-app-ability-childProcess.md#childprocessonstart). The maximum data volume supported by **entryParams** is 150 KB.|
| fds         | Record<string, number> |  No | File Descriptor (FD) handles, which are used for communication between the main process and child process. They are passed to the child process in the form of key-value pairs, where **key** is a custom string and **value** is a DF handle. The FD handles can be obtained through **args.fds** in [ChildProcess.onStart](js-apis-app-ability-childProcess.md#childprocessonstart).<br>NOTE<br>- **fds** supports a maximum of 16 groups. In each group, **key** contains a maximum of 20 characters.<br>- The ID of a handle passed to the child process may change, but the handle always points to the same file.|

**Example**

For details about how to obtain the context in the example, see [Obtaining the Context of UIAbility](../../application-models/uiability-usage.md#obtaining-the-context-of-uiability).

```ts
// In the main process:
import { common, ChildProcessArgs, childProcessManager } from '@kit.AbilityKit';
import fs from '@ohos.file.fs';

let context = getContext(this) as common.UIAbilityContext;
let path = context.filesDir + "/test.txt";
let file = fs.openSync(path, fs.OpenMode.READ_ONLY | fs.OpenMode.CREATE);
let args: ChildProcessArgs = {
  entryParams: "testParam",
  fds: {
    "key1": file.fd
  }
};
childProcessManager.startArkChildProcess("entry/./ets/process/DemoProcess.ets", args);
```

```ts
// In the child process:
import { ChildProcess, ChildProcessArgs } from '@kit.AbilityKit';

export default class DemoProcess extends ChildProcess {

  onStart(args?: ChildProcessArgs) {
    let entryParams = args?.entryParams;
    let fd = args?.fds?.key1;
    // ..
  }
}
```