Coding Guidelines - Visual Studio Code

Overview

This document outlines the coding guidelines for contributing to Visual Studio Code. Following these standards ensures consistency across the codebase and makes it easier for everyone to read and maintain the code.

All contributors are expected to follow these guidelines. Pull requests that don’t adhere to these standards may be asked to make revisions.

Indentation

VS Code uses tabs, not spaces. This is enforced via .editorconfig.

EditorConfig Settings

The project uses EditorConfig to maintain consistent coding styles:

# Tab indentation for all files
[*]
indent_style = tab
trim_trailing_whitespace = true

# Exception: YAML and package.json use 2 spaces
[{*.yml,*.yaml,package.json}]
indent_style = space
indent_size = 2

Why Tabs?

Tabs allow developers to choose their preferred visual width while maintaining consistency in the actual file content. This is a deliberate choice for the VS Code project.

Naming Conventions

Consistent naming makes code more readable and maintainable.

Type Names

Use PascalCase for type names:

type RequestHandler = (request: Request) => Response;

interface EditorOptions {
	tabSize: number;
	insertSpaces: boolean;
}

enum ViewColumn {
	Active = -1,
	Beside = -2,
	One = 1,
	Two = 2
}

Enum Values

Use PascalCase for enum values:

enum FileType {
	File = 1,
	Directory = 2,
	SymbolicLink = 64
}

Functions and Methods

Use camelCase for function and method names:

function parseUri(uri: string): URI {
	// implementation
}

class TextDocument {
	getLineAt(line: number): TextLine {
		// implementation
	}
}

Properties and Variables

Use camelCase for property names and local variables:

const maxLineLength = 100;
let currentPosition = 0;

interface WorkspaceConfiguration {
	lineNumbers: boolean;
	wordWrap: string;
}

Naming Best Practices

Use Whole Words

Prefer complete words over abbreviations when possible:

// Good
const diagnosticCollection = new DiagnosticCollection();

// Avoid
const diagCol = new DiagnosticCollection();

Be Descriptive

Names should clearly indicate what the variable or function does:

// Good
function validateUserInput(input: string): boolean

// Avoid
function check(s: string): boolean

Follow Domain Conventions

Use terminology consistent with VS Code’s domain and existing codebase.

Types

Avoid Polluting Global Namespace

Do not introduce new types or values to the global namespace unless absolutely necessary.

// Good - scoped export
export function parse(content: string): ParsedContent {
	// implementation
}

// Avoid - polluting global scope
declare global {
	function parse(content: string): ParsedContent;
}

Export Minimally

Only export types or functions when you need to share them across multiple components. Keep internal implementation details private.

// Good - internal helper not exported
function normalizeLineEndings(text: string): string {
	return text.replace(/\r\n/g, '\n');
}

export function processDocument(doc: TextDocument): void {
	const content = normalizeLineEndings(doc.getText());
	// ...
}

Avoid `any` and `unknown`

Do not use any or unknown as types for variables, parameters, or return values unless absolutely necessary. Always prefer proper type definitions.

// Good
function parseJson<T>(content: string): T {
	return JSON.parse(content);
}

// Avoid
function parseJson(content: string): any {
	return JSON.parse(content);
}

Comments

Use JSDoc style comments for functions, interfaces, enums, and classes:

/**
 * Represents a text document, such as a source file.
 * Text documents have lines and knowledge about an underlying resource.
 */
interface TextDocument {
	/**
	 * The associated URI for this document.
	 */
	readonly uri: URI;

	/**
	 * Get the text of this document.
	 * @param range The range to get text for. If omitted, returns full document text.
	 * @returns The text in the specified range.
	 */
	getText(range?: Range): string;
}

/**
 * Validates a URI string and returns a normalized URI object.
 * @param uriString The URI string to validate
 * @returns A normalized URI object
 * @throws {Error} If the URI string is invalid
 */
function validateUri(uriString: string): URI {
	// implementation
}

When to Write Comments

Public APIs: Always document with JSDoc
Complex logic: Explain the “why” not the “what”
Non-obvious behavior: Document surprising or unintuitive code
Workarounds: Explain why a workaround is necessary

Avoid comments that simply restate what the code does:

// Bad - comment adds no value
// Increment counter
counter++;

// Good - explains why
// Skip BOM character at start of UTF-8 files
if (content.charCodeAt(0) === 0xFEFF) {
	content = content.substring(1);
}

Strings

Quote Style

VS Code has specific rules for string quotes:

Double Quotes
Single Quotes

Use double quotes for strings shown to the user that need to be externalized (localized):

const message = nls.localize('key', "This message will be translated");

Use single quotes for all other strings:

const filePath = 'src/vs/editor/common/model.ts';
const regex = /[a-z]+/;

Localization

All strings visible to users must be externalized using the vs/nls module:

import * as nls from 'vs/nls';

// Good - externalized with placeholders
const message = nls.localize('fileNotFound', "File '{0}' not found", fileName);

// Avoid - string concatenation
const message = nls.localize('fileNotFound', "File '" + fileName + "' not found");

Externalized strings must not use string concatenation. Always use placeholders like {0}, {1}, etc.

UI Labels

Capitalization

Use title-style capitalization for command labels, buttons, and menu items:

Correct
Incorrect

Open File
Save All
Find in Files
Toggle Developer Tools
Replace with Copy

Don’t capitalize prepositions of four or fewer letters (in, with, for, from) unless it’s the first or last word.

Code Style

Arrow Functions

Prefer arrow functions over anonymous function expressions:

// Good
const numbers = [1, 2, 3].map(n => n * 2);

// Avoid
const numbers = [1, 2, 3].map(function(n) { return n * 2; });

Arrow Function Parameters

Only surround arrow function parameters when necessary:

// Good - single parameter, no parens needed
x => x + x

// Good - multiple parameters need parens
(x, y) => x + y

// Good - type parameters need parens
<T>(x: T, y: T) => x === y

// Wrong - unnecessary parens
(x) => x + x

Curly Braces

Always surround loop and conditional bodies with curly braces:

// Good
if (condition) {
	doSomething();
}

for (let i = 0; i < 10; i++) {
	process(i);
}

// Wrong - missing braces
if (condition)
	doSomething();

for (let i = 0; i < 10; i++)
	process(i);

Brace Placement

Open curly braces always go on the same line:

// Good
if (x < 10) {
	foo();
}

function process(data: string): void {
	// implementation
}

// Wrong
if (x < 10)
{
	foo();
}

Whitespace in Constructs

Parenthesized constructs should have no surrounding whitespace. Single space follows commas, colons, and semicolons:

// Good
for (let i = 0, n = str.length; i < 10; i++) {
	if (x < 10) {
		foo();
	}
}
function f(x: number, y: string): void { }

// Wrong
for ( let i = 0 , n = str.length ; i < 10 ; i++ ) {
	if ( x < 10 ) {
		foo();
	}
}
function f(x:number,y:string):void { }

Function Declaration Style

In top-level scopes, prefer export function x() {} over export const x = () => {}.

Using the function keyword provides better stack traces when debugging:

// Good - shows function name in stack trace
export function validateInput(input: string): boolean {
	// implementation
}

// Less ideal - may show as anonymous in stack traces
export const validateInput = (input: string): boolean => {
	// implementation
};

Code Quality

Async/Await

Prefer async and await over Promise and then calls:

// Good
async function loadDocument(uri: URI): Promise<TextDocument> {
	const content = await readFile(uri);
	const parsed = await parseContent(content);
	return createDocument(parsed);
}

// Avoid
function loadDocument(uri: URI): Promise<TextDocument> {
	return readFile(uri)
		.then(content => parseContent(content))
		.then(parsed => createDocument(parsed));
}

Disposables Management

You MUST deal with disposables by registering them immediately after creation for later disposal.

Use helpers such as DisposableStore, MutableDisposable, or DisposableMap:

// Good - disposables properly managed
class MyComponent {
	private readonly disposables = new DisposableStore();

	constructor() {
		this.disposables.add(workspace.onDidChangeConfiguration(e => {
			// handle change
		}));
	}

	dispose(): void {
		this.disposables.dispose();
	}
}

// Wrong - disposable leak
class MyComponent {
	constructor() {
		workspace.onDidChangeConfiguration(e => {
			// handle change - this listener is never disposed!
		});
	}
}

Do NOT register a disposable to the containing class if the object is created within a method that is called repeatedly. Instead, return an IDisposable and let the caller register it.

File Watching

When adding file watching, prefer correlated file watchers:

// Good - correlated watcher via fileService
const watcher = this.fileService.createWatcher(uri);

// Less ideal - shared watcher
const watcher = this.fileService.watch(uri);

Tooltips

When adding tooltips to UI elements, prefer the IHoverService:

// Good
this.hoverService.showHover({
	content: 'Tooltip content',
	target: element
});

Code Reuse

Do not duplicate code. Always look for existing utility functions, helpers, or patterns before implementing new functionality.

Search Existing Code

Use grep or file search to find similar implementations

Check Common Utilities

Look in src/vs/base/common/ for common utilities

Extend When Possible

Extend existing utilities rather than creating duplicates

Refactor if Needed

If you find duplication, consider refactoring to share code

Storage Keys

You MUST NOT use storage keys of another component only to make changes to that component. Create proper APIs instead.

// Wrong - directly accessing another component's storage
const otherValue = storageService.get('other.component.key');

// Good - using proper API
const otherValue = otherComponent.getValue();

Import Management

Never duplicate imports. Always reuse existing imports if they are present.

// Good
import { URI } from 'vs/base/common/uri';
import { Event } from 'vs/base/common/event';

// Wrong - duplicate imports
import { URI } from 'vs/base/common/uri';
// ... 100 lines later
import { URI } from 'vs/base/common/uri';

Testing

Test Organization

Don’t add tests to the wrong test suite (e.g., adding to end of file instead of inside relevant suite).

Look for existing test patterns before creating new structures:

// Good - organized test suite
suite('TextDocument', () => {
	test('should get line count', () => {
		// test implementation
	});

	test('should get line at position', () => {
		// test implementation
	});
});

Test Assertions

Minimize the number of assertions in tests:

// Good - single comprehensive assertion
test('parse configuration', () => {
	const result = parseConfig(input);
	assert.deepStrictEqual(result, {
		tabSize: 4,
		insertSpaces: false,
		trimTrailingWhitespace: true
	});
});

// Less ideal - multiple fragile assertions
test('parse configuration', () => {
	const result = parseConfig(input);
	assert.strictEqual(result.tabSize, 4);
	assert.strictEqual(result.insertSpaces, false);
	assert.strictEqual(result.trimTrailingWhitespace, true);
});

Regular Expressions

Prefer named capture groups over numbered ones:

// Good - named capture groups
const pattern = /^(?<protocol>https?):\/\/(?<host>[^\/]+)/;
const match = pattern.exec(url);
if (match) {
	const { protocol, host } = match.groups!;
}

// Less ideal - numbered capture groups
const pattern = /^(https?):\/\/([^\/]+)/;
const match = pattern.exec(url);
if (match) {
	const protocol = match[1];
	const host = match[2];
}

Copyright Header

All files must include the Microsoft copyright header at the top.

/*---------------------------------------------------------------------------------------------
 *  Copyright (c) Microsoft Corporation. All rights reserved.
 *  Licensed under the MIT License. See License.txt in the project root for license information.
 *--------------------------------------------------------------------------------------------*/

Cleanup

If you create any temporary files, scripts, or helper files during development:

Document Temporary Files

Keep track of any temporary files you create

Remove Before Committing

Clean up these files before submitting your pull request

Check Git Status

Use git status to ensure no unwanted files are included

Summary

Key Points

Use tabs for indentation
Follow naming conventions (PascalCase for types, camelCase for functions)
Avoid any type
Externalize user-facing strings

Best Practices

Prefer async/await
Manage disposables properly
Reuse existing code
Write comprehensive tests

These guidelines help maintain code quality and consistency across the VS Code codebase. When in doubt, look at existing code for examples.

​Overview

​Indentation

​EditorConfig Settings

​Naming Conventions

​Type Names

​Enum Values

​Functions and Methods

​Properties and Variables

​Naming Best Practices

​Types

​Avoid Polluting Global Namespace

​Export Minimally

​Avoid any and unknown

​Comments

​Strings

​Quote Style

​Localization

​UI Labels

​Capitalization

​Code Style

​Arrow Functions

​Arrow Function Parameters

​Curly Braces

​Brace Placement

​Whitespace in Constructs

​Function Declaration Style

​Code Quality

​Async/Await

​Disposables Management

​File Watching

​Tooltips

​Code Reuse

​Storage Keys

​Import Management

​Testing

​Test Organization

​Test Assertions

​Regular Expressions

​Copyright Header

​Cleanup

​Summary

Key Points

Best Practices

Overview

Indentation

EditorConfig Settings

Naming Conventions

Type Names

Enum Values

Functions and Methods

Properties and Variables

Naming Best Practices

Types

Avoid Polluting Global Namespace

Export Minimally

Avoid `any` and `unknown`

Comments

Strings

Quote Style

Localization

UI Labels

Capitalization

Code Style

Arrow Functions

Arrow Function Parameters

Curly Braces

Brace Placement

Whitespace in Constructs

Function Declaration Style

Code Quality

Async/Await

Disposables Management

File Watching

Tooltips

Code Reuse

Storage Keys

Import Management

Testing

Test Organization

Test Assertions

Regular Expressions

Copyright Header

Cleanup

Summary