# Class: `BaseKernel` [@jupyterlite/kernel](../modules/jupyterlite_kernel.md).BaseKernel A base kernel class handling basic kernel messaging. ## Implements - [`IKernel`](../interfaces/jupyterlite_kernel.IKernel-1.md) ## Constructors ### `constructor` > > **`new BaseKernel`**(`options`) Construct a new BaseKernel. #### Parameters | Name | Type | Description | | :------ | :------ | :------ | | `options` | [`IOptions`](../interfaces/jupyterlite_kernel.IKernel.IOptions.md) | The instantiation options for a BaseKernel. | #### Defined in [packages/kernel/src/kernel.ts:16](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L16) ## Properties ### `_disposed` > > `Private` **`_disposed`**: `Signal`<[`BaseKernel`](jupyterlite_kernel.BaseKernel.md), `void`\> #### Defined in [packages/kernel/src/kernel.ts:632](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L632) ### `_executionCount` > > `Private` **`_executionCount`**: `number` = `0` #### Defined in [packages/kernel/src/kernel.ts:630](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L630) ### `_history` > > `Private` **`_history`**: [`number`, `number`, `string`][] = `[]` #### Defined in [packages/kernel/src/kernel.ts:629](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L629) ### `_id` > > `Private` **`_id`**: `string` #### Defined in [packages/kernel/src/kernel.ts:626](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L626) ### `_isDisposed` > > `Private` **`_isDisposed`**: `boolean` = `false` #### Defined in [packages/kernel/src/kernel.ts:631](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L631) ### `_location` > > `Private` **`_location`**: `string` #### Defined in [packages/kernel/src/kernel.ts:628](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L628) ### `_name` > > `Private` **`_name`**: `string` #### Defined in [packages/kernel/src/kernel.ts:627](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L627) ### `_parent` > > `Private` **`_parent`**: `undefined` \| `IMessage`<`MessageType`\> = `undefined` #### Defined in [packages/kernel/src/kernel.ts:636](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L636) ### `_parentHeader` > > `Private` **`_parentHeader`**: `undefined` \| `IHeader`<`MessageType`\> = `undefined` #### Defined in [packages/kernel/src/kernel.ts:634](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L634) ### `_sendMessage` > > `Private` **`_sendMessage`**: [`SendMessage`](../modules/jupyterlite_kernel.IKernel.md#sendmessage) #### Defined in [packages/kernel/src/kernel.ts:633](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L633) ## Accessors ### `disposed` > > `get` **`disposed`**(): `ISignal`<`this`, `void`\> A signal emitted when the kernel is disposed. #### Returns `ISignal`<`this`, `void`\> #### Implementation of [IKernel](../interfaces/jupyterlite_kernel.IKernel-1.md).[disposed](../interfaces/jupyterlite_kernel.IKernel-1.md#disposed) #### Defined in [packages/kernel/src/kernel.ts:41](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L41) ### `executionCount` > > `get` **`executionCount`**(): `number` The current execution count #### Returns `number` #### Defined in [packages/kernel/src/kernel.ts:69](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L69) ### `id` > > `get` **`id`**(): `string` Get the kernel id #### Returns `string` #### Implementation of [IKernel](../interfaces/jupyterlite_kernel.IKernel-1.md).[id](../interfaces/jupyterlite_kernel.IKernel-1.md#id) #### Defined in [packages/kernel/src/kernel.ts:48](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L48) ### `isDisposed` > > `get` **`isDisposed`**(): `boolean` Return whether the kernel is disposed. #### Returns `boolean` #### Implementation of [IKernel](../interfaces/jupyterlite_kernel.IKernel-1.md).[isDisposed](../interfaces/jupyterlite_kernel.IKernel-1.md#isdisposed) #### Defined in [packages/kernel/src/kernel.ts:34](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L34) ### `location` > > `get` **`location`**(): `string` The location in the virtual filesystem from which the kernel was started. #### Returns `string` #### Implementation of [IKernel](../interfaces/jupyterlite_kernel.IKernel-1.md).[location](../interfaces/jupyterlite_kernel.IKernel-1.md#location) #### Defined in [packages/kernel/src/kernel.ts:62](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L62) ### `name` > > `get` **`name`**(): `string` Get the name of the kernel #### Returns `string` #### Implementation of [IKernel](../interfaces/jupyterlite_kernel.IKernel-1.md).[name](../interfaces/jupyterlite_kernel.IKernel-1.md#name) #### Defined in [packages/kernel/src/kernel.ts:55](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L55) ### `parent` > > `get` **`parent`**(): `undefined` \| `IMessage`<`MessageType`\> Get the last parent message (mimic ipykernel's get_parent) #### Returns `undefined` \| `IMessage`<`MessageType`\> #### Defined in [packages/kernel/src/kernel.ts:83](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L83) ### `parentHeader` > > `get` **`parentHeader`**(): `undefined` \| `IHeader`<`MessageType`\> Get the last parent header #### Returns `undefined` \| `IHeader`<`MessageType`\> #### Defined in [packages/kernel/src/kernel.ts:76](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L76) ### `ready` > > `get` **`ready`**(): `Promise`<`void`\> A promise that is fulfilled when the kernel is ready. #### Returns `Promise`<`void`\> #### Implementation of [IKernel](../interfaces/jupyterlite_kernel.IKernel-1.md).[ready](../interfaces/jupyterlite_kernel.IKernel-1.md#ready) #### Defined in [packages/kernel/src/kernel.ts:27](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L27) ## Methods ### `_busy` > > `Private` **`_busy`**(`parent`): `void` Send a 'busy' status message. #### Parameters | Name | Type | Description | | :------ | :------ | :------ | | `parent` | `IMessage`<`MessageType`\> | The parent message. | #### Returns `void` #### Defined in [packages/kernel/src/kernel.ts:463](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L463) ### `_complete` > > `Private` **`_complete`**(`msg`): `Promise`<`void`\> Handle an complete_request message #### Parameters | Name | Type | Description | | :------ | :------ | :------ | | `msg` | `IMessage`<`MessageType`\> | The parent message. | #### Returns `Promise`<`void`\> #### Defined in [packages/kernel/src/kernel.ts:574](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L574) ### `_execute` > > `Private` **`_execute`**(`msg`): `Promise`<`void`\> Handle an execute_request message. #### Parameters | Name | Type | Description | | :------ | :------ | :------ | | `msg` | `IMessage`<`MessageType`\> | The parent message. | #### Returns `Promise`<`void`\> #### Defined in [packages/kernel/src/kernel.ts:541](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L541) ### `_executeInput` > > `Private` **`_executeInput`**(`msg`): `void` Send an `execute_input` message. #### Parameters | Name | Type | Description | | :------ | :------ | :------ | | `msg` | `IMessage`<`MessageType`\> | The parent message. | #### Returns `void` #### Defined in [packages/kernel/src/kernel.ts:520](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L520) ### `_historyRequest` > > `Private` **`_historyRequest`**(`msg`): `Promise`<`void`\> Handle a `history_request` message #### Parameters | Name | Type | Description | | :------ | :------ | :------ | | `msg` | `IMessage`<`MessageType`\> | The parent message. | #### Returns `Promise`<`void`\> #### Defined in [packages/kernel/src/kernel.ts:500](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L500) ### `_idle` > > `Private` **`_idle`**(`parent`): `void` Send an 'idle' status message. #### Parameters | Name | Type | Description | | :------ | :------ | :------ | | `parent` | `IMessage`<`MessageType`\> | The parent message | #### Returns `void` #### Defined in [packages/kernel/src/kernel.ts:445](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L445) ### `_inspect` > > `Private` **`_inspect`**(`msg`): `Promise`<`void`\> Handle an inspect_request message #### Parameters | Name | Type | Description | | :------ | :------ | :------ | | `msg` | `IMessage`<`MessageType`\> | The parent message. | #### Returns `Promise`<`void`\> #### Defined in [packages/kernel/src/kernel.ts:593](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L593) ### `_isCompleteRequest` > > `Private` **`_isCompleteRequest`**(`msg`): `Promise`<`void`\> Handle an is_complete_request message #### Parameters | Name | Type | Description | | :------ | :------ | :------ | | `msg` | `IMessage`<`MessageType`\> | The parent message. | #### Returns `Promise`<`void`\> #### Defined in [packages/kernel/src/kernel.ts:612](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L612) ### `_kernelInfo` > > `Private` **`_kernelInfo`**(`parent`): `Promise`<`void`\> Handle a kernel_info_request message #### Parameters | Name | Type | Description | | :------ | :------ | :------ | | `parent` | `IMessage`<`MessageType`\> | The parent message. | #### Returns `Promise`<`void`\> #### Defined in [packages/kernel/src/kernel.ts:481](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L481) ### `clearOutput` > > `Protected` **`clearOutput`**(`content`, `parentHeader?`): `void` Send a `clear_output` message to the client. #### Parameters | Name | Type | Default value | Description | | :------ | :------ | :------ | :------ | | `content` | `Object` | `undefined` | The clear_output content. | | `content.wait` | `boolean` | `undefined` | - | | `parentHeader` | `undefined` \| `IHeader`<`MessageType`\> | `undefined` | The parent header. | #### Returns `void` #### Defined in [packages/kernel/src/kernel.ts:392](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L392) ### `commClose` > > `Abstract` **`commClose`**(`msg`): `Promise`<`void`\> Send an `comm_close` message. #### Parameters | Name | Type | | :------ | :------ | | `msg` | `ICommCloseMsg`<``"shell"`` \| ``"iopub"``\> | #### Returns `Promise`<`void`\> #### Defined in [packages/kernel/src/kernel.ts:231](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L231) ### `commInfoRequest` > > `Abstract` **`commInfoRequest`**(`content`): `Promise`<`ReplyContent`<`ICommInfoReply`\>\> Handle a `comm_info_request` message. #### Parameters | Name | Type | Description | | :------ | :------ | :------ | | `content` | `Object` | The content of the request. | | `content.target_name?` | `string` | The comm target name to filter returned comms | #### Returns `Promise`<`ReplyContent`<`ICommInfoReply`\>\> A promise that resolves with the response message. #### Defined in [packages/kernel/src/kernel.ts:201](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L201) ### `commMsg` > > `Abstract` **`commMsg`**(`msg`): `Promise`<`void`\> Send an `comm_msg` message. #### Parameters | Name | Type | Description | | :------ | :------ | :------ | | `msg` | `ICommMsgMsg`<``"shell"`` \| ``"iopub"``\> | The comm_msg message. | #### Returns `Promise`<`void`\> #### Defined in [packages/kernel/src/kernel.ts:224](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L224) ### `commOpen` > > `Abstract` **`commOpen`**(`msg`): `Promise`<`void`\> Send an `comm_open` message. #### Parameters | Name | Type | Description | | :------ | :------ | :------ | | `msg` | `ICommOpenMsg`<``"shell"`` \| ``"iopub"``\> | The comm_open message. | #### Returns `Promise`<`void`\> #### Defined in [packages/kernel/src/kernel.ts:217](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L217) ### `completeRequest` > > `Abstract` **`completeRequest`**(`content`): `Promise`<`ReplyContent`<`ICompleteReply`\>\> Handle a `complete_request` message. #### Parameters | Name | Type | Description | | :------ | :------ | :------ | | `content` | `Object` | The content of the request. | | `content.code` | `string` | - | | `content.cursor_pos` | `number` | - | #### Returns `Promise`<`ReplyContent`<`ICompleteReply`\>\> #### Defined in [packages/kernel/src/kernel.ts:168](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L168) ### `displayData` > > `Protected` **`displayData`**(`content`, `parentHeader?`): `void` Send a `display_data` message to the client. #### Parameters | Name | Type | Default value | Description | | :------ | :------ | :------ | :------ | | `content` | `Object` | `undefined` | The display_data content. | | `content.data` | `IMimeBundle` | `undefined` | - | | `content.metadata` | `PartialJSONObject` | `undefined` | - | | `content.transient?` | `Object` | `undefined` | - | | `content.transient.display_id?` | `string` | `undefined` | - | | `parentHeader` | `undefined` \| `IHeader`<`MessageType`\> | `undefined` | The parent header. | #### Returns `void` #### Defined in [packages/kernel/src/kernel.ts:264](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L264) ### `dispose` > > **`dispose`**(): `void` Dispose the kernel. #### Returns `void` #### Implementation of [IKernel](../interfaces/jupyterlite_kernel.IKernel-1.md).[dispose](../interfaces/jupyterlite_kernel.IKernel-1.md#dispose) #### Defined in [packages/kernel/src/kernel.ts:90](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L90) ### `executeRequest` > > `Abstract` **`executeRequest`**(`content`): `Promise`<`Object`\> Handle an `execute_request` message. #### Parameters | Name | Type | Description | | :------ | :------ | :------ | | `content` | `Object` | The content of the execute_request kernel message | | `content.allow_stdin?` | `boolean` | Whether to allow stdin requests. The default is `true`. | | `content.code` | `string` | The code to execute. | | `content.silent?` | `boolean` | Whether to execute the code as quietly as possible. The default is `false`. | | `content.stop_on_error?` | `boolean` | Whether to the abort execution queue on an error. The default is `false`. | | `content.store_history?` | `boolean` | Whether to store history of the execution. The default `true` if silent is False. It is forced to `false ` if silent is `true`. | | `content.user_expressions?` | `JSONObject` | A mapping of names to expressions to be evaluated in the kernel's interactive namespace. | #### Returns `Promise`<`Object`\> #### Defined in [packages/kernel/src/kernel.ts:159](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L159) ### `handleComm` > > `Protected` **`handleComm`**(`type`, `content`, `metadata`, `buffers`, `parentHeader?`): `void` Send a `comm` message to the client. #### Parameters | Name | Type | Default value | | :------ | :------ | :------ | | `type` | ``"comm_close"`` \| ``"comm_msg"`` \| ``"comm_open"`` | `undefined` | | `content` | `Object` | `undefined` | | `content.comm_id` | `string` | `undefined` | | `content.data` | `JSONObject` | `undefined` | | `metadata` | `JSONObject` | `undefined` | | `buffers` | `undefined` \| (`ArrayBuffer` \| `ArrayBufferView`)[] | `undefined` | | `parentHeader` | `undefined` \| `IHeader`<`MessageType`\> | `undefined` | #### Returns `void` #### Defined in [packages/kernel/src/kernel.ts:416](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L416) ### `handleMessage` > > **`handleMessage`**(`msg`): `Promise`<`void`\> Handle an incoming message from the client. #### Parameters | Name | Type | Description | | :------ | :------ | :------ | | `msg` | `IMessage`<`MessageType`\> | The message to handle | #### Returns `Promise`<`void`\> #### Implementation of [IKernel](../interfaces/jupyterlite_kernel.IKernel-1.md).[handleMessage](../interfaces/jupyterlite_kernel.IKernel-1.md#handlemessage) #### Defined in [packages/kernel/src/kernel.ts:103](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L103) ### `inputReply` > > `Abstract` **`inputReply`**(`content`): `void` Send an `input_reply` message. #### Parameters | Name | Type | Description | | :------ | :------ | :------ | | `content` | `ReplyContent`<`IInputReply`\> | The content of the reply. | #### Returns `void` #### Defined in [packages/kernel/src/kernel.ts:210](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L210) ### `inputRequest` > > `Protected` **`inputRequest`**(`content`, `parentHeader?`): `void` Send a `input_request` message to the client. #### Parameters | Name | Type | Default value | Description | | :------ | :------ | :------ | :------ | | `content` | `Object` | `undefined` | The input_request content. | | `content.password` | `boolean` | `undefined` | Whether the request is for a password. If so, the frontend shouldn't echo input. | | `content.prompt` | `string` | `undefined` | The text to show at the prompt. | | `parentHeader` | `undefined` \| `IHeader`<`MessageType`\> | `undefined` | The parent header. | #### Returns `void` #### Defined in [packages/kernel/src/kernel.ts:292](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L292) ### `inspectRequest` > > `Abstract` **`inspectRequest`**(`content`): `Promise`<`ReplyContent`<`IInspectReply`\>\> Handle an `inspect_request` message. #### Parameters | Name | Type | Description | | :------ | :------ | :------ | | `content` | `Object` | The content of the request. | | `content.code` | `string` | - | | `content.cursor_pos` | `number` | - | | `content.detail_level` | ``0`` \| ``1`` | - | #### Returns `Promise`<`ReplyContent`<`IInspectReply`\>\> A promise that resolves with the response message. #### Defined in [packages/kernel/src/kernel.ts:179](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L179) ### `isCompleteRequest` > > `Abstract` **`isCompleteRequest`**(`content`): `Promise`<`ReplyContent`<`IIsCompleteReplyIncomplete` \| `IIsCompleteReplyOther`\>\> Handle an `is_complete_request` message. #### Parameters | Name | Type | Description | | :------ | :------ | :------ | | `content` | `Object` | The content of the request. | | `content.code` | `string` | - | #### Returns `Promise`<`ReplyContent`<`IIsCompleteReplyIncomplete` \| `IIsCompleteReplyOther`\>\> A promise that resolves with the response message. #### Defined in [packages/kernel/src/kernel.ts:190](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L190) ### `kernelInfoRequest` > > `Abstract` **`kernelInfoRequest`**(): `Promise`<`ReplyContent`<`IInfoReply`\>\> Handle a `kernel_info_request` message. #### Returns `Promise`<`ReplyContent`<`IInfoReply`\>\> A promise that resolves with the kernel info. #### Defined in [packages/kernel/src/kernel.ts:152](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L152) ### `publishExecuteError` > > `Protected` **`publishExecuteError`**(`content`, `parentHeader?`): `void` Send an `error` message to the client. #### Parameters | Name | Type | Default value | Description | | :------ | :------ | :------ | :------ | | `content` | `Object` | `undefined` | The error content. | | `content.ename` | `string` | `undefined` | - | | `content.evalue` | `string` | `undefined` | - | | `content.traceback` | `string`[] | `undefined` | - | | `parentHeader` | `undefined` \| `IHeader`<`MessageType`\> | `undefined` | The parent header. | #### Returns `void` #### Defined in [packages/kernel/src/kernel.ts:342](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L342) ### `publishExecuteResult` > > `Protected` **`publishExecuteResult`**(`content`, `parentHeader?`): `void` Send an `execute_result` message. #### Parameters | Name | Type | Default value | Description | | :------ | :------ | :------ | :------ | | `content` | `Object` | `undefined` | The execute result content. | | `content.data` | `IMimeBundle` | `undefined` | - | | `content.execution_count` | `ExecutionCount` | `undefined` | - | | `content.metadata` | `PartialJSONObject` | `undefined` | - | | `content.transient?` | `Object` | `undefined` | - | | `content.transient.display_id?` | `string` | `undefined` | - | | `parentHeader` | `undefined` \| `IHeader`<`MessageType`\> | `undefined` | The parent header. | #### Returns `void` #### Defined in [packages/kernel/src/kernel.ts:317](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L317) ### `stream` > > `Protected` **`stream`**(`content`, `parentHeader?`): `void` Stream an event from the kernel #### Parameters | Name | Type | Default value | Description | | :------ | :------ | :------ | :------ | | `content` | `Object` | `undefined` | The stream content. | | `content.name` | ``"stdout"`` \| ``"stderr"`` | `undefined` | - | | `content.text` | `string` | `undefined` | - | | `parentHeader` | `undefined` \| `IHeader`<`MessageType`\> | `undefined` | The parent header. | #### Returns `void` #### Defined in [packages/kernel/src/kernel.ts:239](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L239) ### `updateDisplayData` > > `Protected` **`updateDisplayData`**(`content`, `parentHeader?`): `void` Send a `update_display_data` message to the client. #### Parameters | Name | Type | Default value | Description | | :------ | :------ | :------ | :------ | | `content` | { `data`: `IMimeBundle` ; `metadata`: `PartialJSONObject` ; `transient?`: { `display_id?`: `string` } } & { `transient`: { `display_id`: `string` } } | `undefined` | The update_display_data content. | | `parentHeader` | `undefined` \| `IHeader`<`MessageType`\> | `undefined` | The parent header. | #### Returns `void` #### Defined in [packages/kernel/src/kernel.ts:367](https://github.com/jupyterlite/jupyterlite/blob/55b565b/packages/kernel/src/kernel.ts#L367)