Communicate language server with client in VSCode extension

vscode extension - published at 14/08/2023

In vscode extension, language client can send messeages with client.sendRequest and language server can receive them with connection.onRequest.

// shared/requests.ts
import { RequestType } from 'vscode-jsonrpc/node';

export type MyPackageFooRequestParams = {
  someArg: string;
export const MyPackageFooRequestType = new RequestType<
  // payload
  // return type
// client
const params: MyPackageFooRequestParams = {
  someArg: 'anything',
const res = await client.sendRequest(MyPackageFooRequestType, params);
// server
connection.onRequest(MyPackageFooRequestType, async (params) => {
  const { someArg } = params;

  // do something...

  // send back to client
  return 'anything';

RequestType can be imported from vscode-languageclient/node and vscode-languageserver/node, but if you want to share the code, I recommend to import from vscode-jsonrpc, which is internally used in both vscode-languageclient/node and vscode-languageserver/node.