TypeScript Language Server

• What is it, exactly?
• Installing
• Running the language server
• CLI Options
• Configuration
• Features
  • Code actions on save
  • Workspace commands (workspace/executeCommand)
    • Go to Source Definition
    • Apply Refactoring
    • Organize Imports
    • Rename File
    • Send Tsserver Command
    • Configure plugin
  • Code Lenses (textDocument/codeLens)
  • Inlay hints (textDocument/inlayHint)
  • TypeScript Version Notification
  • Workspace Configuration request for formatting settings
• Development
  • Build
  • Dev
  • Test
  • Publishing

What is it, exactly?

The TypeScript project/package includes a tsserver component which provides a custom API that can be used for gathering various intelligence about a typescript/javascript project. The VSCode team has built a project called Typescript Language Features (and bundled it as an internal extension in VSCode) that provides code intelligence for your javascript and typescript projects by utilizing that tsserver API. Since that extension doesn't use the standardized Language Server Protocol to communicate with the editor, other editors that implement LSP can't directly utilize it. Here is where the TypeScript Language Server project comes in with the aim to provide a thin LSP interface on top of that extension's code base for the benefit of all other editors that implement the LSP protocol.

Originally based on concepts and ideas from https://github.com/prabirshrestha/typescript-language-server and maintained by TypeFox. Currently maintained by a community of contributors like you.

This project is not directly associated with Microsoft and is not used in their VSCode editor. If you have an issue with VSCode functionality, report it in their repository instead.

Currently Microsoft is working on TypeScript 7 written natively in the go language that will include the LSP implementation and will hopefully supersede this project.

Installing

npm install -g typescript-language-server typescript

Running the language server

typescript-language-server --stdio

CLI Options

  Usage: typescript-language-server [options]


  Options:

    -V, --version                          output the version number
    --stdio                                use stdio (required option)
    --log-level <log-level>                A number indicating the log level (4 = log, 3 = info, 2 = warn, 1 = error). Defaults to `3`.
    -h, --help                             output usage information

Configuration

See configuration documentation.

Features

Code actions on save

Server announces support for the following code action kinds:

• source.fixAll.ts - despite the name, fixes a couple of specific issues: unreachable code, await in non-async functions, incorrectly implemented interface
• source.removeUnused.ts - removes declared but unused variables
• source.addMissingImports.ts - adds imports for used but not imported symbols
• source.removeUnusedImports.ts - removes unused imports
• source.sortImports.ts - sorts imports
• source.organizeImports.ts - organizes and removes unused imports

This allows editors that support running code actions on save to automatically run fixes associated with those kinds.

Those code actions, if they apply in the current code, should also be presented in the list of "Source Actions" if the editor exposes those.

The user can enable it with a setting similar to (can vary per-editor):

"codeActionsOnSave": {
    "source.organizeImports.ts": true,
    // or just
    "source.organizeImports": true,
}

Workspace commands (workspace/executeCommand)

See LSP specification.

Most of the time, you'll execute commands with arguments retrieved from another request like textDocument/codeAction. There are some use cases for calling them manually.

lsp refers to the language server protocol types, tsp refers to the typescript server protocol types.

Go to Source Definition

Request:

{
    command: '_typescript.goToSourceDefinition'
    arguments: [
        lsp.DocumentUri,  // String URI of the document
        lsp.Position,     // Line and character position (zero-based)
    ]
}

Response:

lsp.Location[] | null

(This command is supported from Typescript 4.7.)

Apply Refactoring

Request:

{
    command: '_typescript.applyRefactoring'
    arguments: [
        tsp.GetEditsForRefactorRequestArgs,
    ]
}

Response:

void

Organize Imports

Request:

{
    command: '_typescript.organizeImports'
    arguments: [
        string,  // file path
        // Optional options:
        {
            // @deprecated - use "mode". Supported from Typescript 4.4+.
            skipDestructiveCodeActions?: boolean
            // 'All' - organizes imports including destructive actions (removing unused imports)
            // 'SortAndCombine' - Doesn't perform destructive actions.
            // 'RemoveUnused' - Only removes unused imports.
            mode?: 'All' | 'SortAndCombine' | 'RemoveUnused'
        },
    ]
}

Response:

void

Rename File

Request:

{
    command: '_typescript.applyRenameFile'
    arguments: [
        { sourceUri: string; targetUri: string; },
    ]
}

Response:

void

Send Tsserver Command

Request:

{
    command: 'typescript.tsserverRequest'
    arguments: [
        string,       // command
        any,          // command arguments in a format that the command expects
        ExecuteInfo,  // configuration object used for the tsserver request (see below)
    ]
}

Response:

any

The ExecuteInfo object is defined as follows:

type ExecuteInfo = {
    executionTarget?: number;  // 0 - semantic server, 1 - syntax server; default: 0
    expectsResult?: boolean;   // default: true
    isAsync?: boolean;         // default: false
    lowPriority?: boolean;     // default: true
};

Configure plugin

Request:

{
    command: '_typescript.configurePlugin'
    arguments: [pluginName: string, configuration: any]
}

Response:

void

Code Lenses (textDocument/codeLens)

Code lenses can be enabled using the implementationsCodeLens and referencesCodeLens workspace configuration options.

Code lenses provide a count of references and/or implemenations for symbols in the document. For clients that support it it's also possible to click on those to navigate to the relevant locations in the the project. Do note that clicking those trigger a editor.action.showReferences command which is something that client needs to have explicit support for. Many do by default but some don't. An example command will look like this:

command: {
    title: '1 reference',
    command: 'editor.action.showReferences',
    arguments: [
        'file://project/foo.ts',    // URI
        { line: 1, character: 1 },  // Position
        [                           // A list of Location objects.
            {
                uri: 'file://project/bar.ts',
                range: {
                    start: {
                        line: 7,
                        character: 24,
                    },
                    end: {
                        line: 7,
                        character: 28,
                    },
                },
            },
        ],
    ],
}

Inlay hints (textDocument/inlayHint)

For the request to return any results, some or all of the following options need to be enabled through preferences:

export interface InlayHintsOptions extends UserPreferences {
    includeInlayParameterNameHints: 'none' | 'literals' | 'all';
    includeInlayParameterNameHintsWhenArgumentMatchesName: boolean;
    includeInlayFunctionParameterTypeHints: boolean;
    includeInlayVariableTypeHints: boolean;
    includeInlayVariableTypeHintsWhenTypeMatchesName: boolean;
    includeInlayPropertyDeclarationTypeHints: boolean;
    includeInlayFunctionLikeReturnTypeHints: boolean;
    includeInlayEnumMemberValueHints: boolean;
}

TypeScript Version Notification

Right after initializing, the server sends a custom $/typescriptVersion notification that carries information about the version of TypeScript that is utilized by the server. The editor can then display that information in the UI.

The $/typescriptVersion notification params include two properties:

• version - a semantic version (for example 4.8.4)
• source - a string specifying whether used TypeScript version comes from the local workspace (workspace), is explicitly specified through a initializationOptions.tsserver.path setting (user-setting) or was bundled with the server (bundled)

Workspace Configuration request for formatting settings

Server asks the client (provided client supports workspace/configuration capability) for file-specific configuration options (tabSize and insertSpaces) that are required by tsserver to properly format file edits when for example using "Organize imports" or performing other file modifications. Those options have to be dynamically provided by the client/editor since the values can differ for each file. For this reason server sends a workspace/configuration request with scopeUri equal to file's URI and section equal to formattingOptions. The client is expected to return a configuration that includes the following properties:

{
    "tabSize": number
    "insertSpaces": boolean
}

Development

Build

yarn build

Dev

Build and rebuild on change.

yarn dev

Test

• yarn test - run all tests in watch mode for developing
• yarn test:commit - run all tests once

By default only console logs of level warning and higher are printed to the console. You can override the CONSOLE_LOG_LEVEL level in package.json to either log, info, warning or error to log other levels.

Publishing

The project uses https://github.com/google-github-actions/release-please-action Github action to automatically release new version on merging a release PR.